3rd Rock from the Sun: A joke in the pilot episode. Mary engages in a literal Slap-Slap-Kiss with Dick, and — being an alien with limited understanding of human culture — he follows her lead and smacks her after the second kiss. (And then leaving the party, he responds the same way to the poor hostess kissing him on the cheek.)
24: Even though his kills can be counted on one hand, Jack Bauer is just as willing to kill female terrorists as he is the male ones. Or torture or wounding them for that matter if it means accomplishing his goals, even if they're innocent.
30 Rock: This show is one of the few shows that plays men hitting women for slapstick humor:
Dr. Spaceman: GO TO SLEEP! SLEEP, JENNA! SLEEP! IT'S FOR YOUR OWN GOOD!
Several episodes feature officers Malloy and Reed responding to domestic disputes; the very end of the male protagonist hitting the woman — before the officers break it up — is seen in at least a couple of episodes.
In the episode "X-Force," both Malloy and Reed spot an unconscious 6-year-old girl in the living room of a suspected child rapist; the girl is not seen explicitly on screen, but the reactions of our two protagonist officers make it clear what they witnessed. (Malloy is so disgusted that later, when the suspect makes a smart remark about how his victim got what she wanted, he blows his top.)
Adam Adamant Lives: The title character is notable for being so chivalrous that he refuses to believe any woman could be a villain, even though there's a female villain in virtually every episode. When he is presented with evidence of their duplicity, however, he doesn't tend to pull his punches: the very first episode ends with him pushing a female villain off a roof when she threatens Georgina, noting he's never killed a woman before but she's forced him to do so.
Alphas: Both Bill and Cameron have no problem beating up Dark Action Girls, which is a good thing as until the second season all of the women with combat powers are evil.
Better Off Ted: Veronica goes through a period of slapping her problems in the face. When she slaps Ted, he slaps her right back. Her reaction: "We're cool."
Blakes Seven: Avon has no qualms about hitting, or killing, anyone who is a threat to his continued existence. Most blatant times are in "Mission to Destiny" where he suckerpunches an extremely annoying woman who was going to sell everyone out (which he "quite enjoyed"), and in "Rumours of Death" when he kills Anna Grant.
Also applies to Blake, though he won't hit a woman before she hits him.
In the 14th-season opener, "Forever," Little Joe finally gets married to a beautiful young woman named Alice. However, Alice's brother is an indolent gambler being stalked by a ruthless gambler named Sloan and his thugs ... and they eventually learn that Alice has married into the wealthy Cartwright family and have more than enough money to pay off Sloan. When Alice refuses and one of Sloan's stooges tries to steal a music box, she resists and flees to the bedroom ... only for the designated giant of the group (a 6-foot-8, 300-pound muscle man) to stalk Alice. Although not seen on camera, it is later implied that the giant brutally beat Alice (5-foot-5 and 120 pounds tops) by slapping and punching her repeatedly and crushing her ribs, before breaking her neck and killing her ... all this before the baddies burned down the house that she and Joe shared. (Incidentally, "Forever" was meant to showcase Dan Blocker as Hoss was the intended bridegroom, but Blocker's sudden death in May 1972 forced hasty rewrites by episode writer Michael Landon ... and his decision to put Joe in the shoes of Alice's husband-to-be.)
Despite the lack of male-on-female violence — the scene had ended with Alice looking scared, before a cut back to a ranch scene (Joe and the others unaware of what's going on at his house) — CBN, which once reran Bonanza, refused to air the episode due to the implied violence.
Nobody had a problem trying to hit Buffy. However, very few actually managed to lay a hand on her Good Old Fisticuffs style, and those powerful enough to usually relied on magic attacks and weapons. Notable exceptions are Spike (which eventually transforms into foreplay when Buffy and him become a couple), Caleb, and Angel (who slugs Buffy after she's asked him to do so during a sparring match.)
Sam Axe. Turns out he will hit a girl if she's trying to take away his shotgun, even if only after a fair bit of provocation.
Another episode had Michael slapping Fiona across the face in order to maintain a cover. He was quite apologetic, however.
Possibly because Fiona is an Axe Crazy woman who keeps C-4 in the trunk of her car. Michael was hovering over the line between being apologetic and being afraid of her.
and Michael will hit a female assassin attacking him with a knife in the face with a steel lined briefcase.
Michael will also shoot a woman, although in this case she shot him first (he was wearing a kevlar undershirt, though), and he only hit her in the shoulder. Of course, said woman is a trained assassin and, at the time, he thought she killed his brother.
There was also the time he had to hit his mother. They were all undercover, trying to get a captured bad guy to talk, and Madeline was playing a nurse brought in to play good cop. They decide to really sell that Michael was the bigger threat and get him to snitch, and Madeline came up with the idea of "why doesn't he just hit me." Since they both lived in an abusive household for years, it was uncomfortable on all sides.
The Charmed ones pose a threat to every demon in existence so any worries they have about hitting women goes out the window, especially when one of them is trained in martial arts. Cole shows no problem training hand-to-hand with Phoebe and he eventually does hit her in the fifth season (in a bad future where they're still together but miserable).
John Casey will not hesitate to attack a female enemy, and is implied by sheer amount of force used to have killed one or two.
Another notable example is when one episode where a large bad guy named Hugo Panzer breaks out of Castle and is confronted by Agent Greta. Greta attempts to take him down with a swift kick from her long legs, which doesn't even faze him. Panzer then responds by knocking her out with one punch. (The scene was all the more memorable due to both characters being played by well-known wrestlers).
COPS: Several episodes have depicted male-on-female violence, with the officers responding to stop the proceedings.
Criminal Minds: Does this a lot. Usually it's done so the UnSub can gain control of the victim in question, but sometimes- such as in "Minimal Loss" when Emily Prentiss allows herself to get smacked around (or is actually overpowered in a fight by Ian Doyle) and the final victim who was rescued in "The Slave of Duty"- the Big Bad gets to actually partake in a beating.
Danger 5: In the episode "Fresh Meat for Hitler's Sex Kitchen", Jackson decks a Nazi woman who is trying to kiss him.
Jackson: Get your fascist mouth away from me!
Nazi Woman: You hit a woman!
Jackson: I hit a Nazi.
Dog The Bounty Hunter: Several of the bail jumpers pursued are alleged to have committed violence against women. One of them even threw Lyssa Chapman to the ground when she attempted to apprehend him.
EastEnders: One episode featured a heated argument between Sharon and Phil. Sharon slapped Phil, resulting in a few half-hearted gasps from the people around. Phil hit her back. Cue outcry, with people dragging him back and screaming "you can't hit a girl!".
Game of Thrones: Being a Crapsack World, there are many men, even supposed chivalrous knights, who are ready, willing, and able to hurt women. Most significantly, Ser Meryn Trant beat a helpless Sansa Stark at the behest of King Joffrey whenever she displeased him. To be fair, some women in the series are able to hit back.
Glee: In Season One, Karofsky casually shoves Tina into Kurt when the two of them are wearing their Lady Gaga outfits, only to get told off by a scared but determined Kurt for hitting a girl. By the second season, however, Karofsky has moved into both Armored Closet Gay and Stalker with a Crush territory, and ignores Tina to shove Kurt, who is walking with her, into the lockers.
Heroes: In season one, Nikki Sanders meets Nathan Petrelli a second time and warns him that he's walking into a trap. Then she tells him to knock her out. Nathan hesitates, and Nikki tells him that if he doesn't, Jessica will take control again. So, Nathan punches her in the face.
Highlander: Methos had no problem hitting, or even killing women. And while he was morally ambiguous sometimes, he definitely fell on the gender/sexual equality end of this trope:
Kristin Gilles: "Who the hell are you?!"
Methos: "A man born long before the age of chivalry."
Human Target: Guerrero pretty much introduced himself to Ames by punching her in the face. (It wasn't totally unreasonable in context, but it also wasn't his only option.)
Jersey Shore: Had a moment early in its first season when a patron at the bar that the group was at took their drinks. Snooki went over to tell the guy that the drinks were theirs and he randomly punched her in the face. This got him in a heap of trouble, not only getting him arrested but also nearly beat up on the street by a bunch of other bargoers that were gonna mess him up for hitting a girl.
Modern Riders have absolutely no qualms about fighting female monsters regardless of alignment, a stark contrast to old-school Riders, who are reluctant to fight women. That said, female monsters are still pretty rare.
In a more specific example, Kamen Rider Double's second movie features a woman as part of the villainous mercenaries set on taking over the city. Shotaro doesn't fight her as a human because she's a better fighter and has flame powers, but when they're transformed the playing field is more even and he fights back.
Leverage: When the team faces their Evil Counterparts, Eliot's is an Israeli woman. When they finally fight for real, she asks "You wouldn't hit a girl, would you?" and he responds in Hebrew "Not unless she hits me first." When she does, he says "That counts" and they fight, with a lot of Clothing Damageon both sides.
Life on Mars (2006): Discussed. While Gene seems to draw the line at striking women, he isn't averse to using other aggressive tactics on them. One episode features a suspect who was seen pushing a woman out of a car; Gene defends him against Sam's accusations by saying that doesn't make one 'a bad bloke'.
Little House on the Prairie: Several villains and antagonists hit women and girls in various women. The actual assault is rarely, if ever seen on camera, as cutaways are often used and it is stunt doubles who take the actual blows.
Lois and Clark: Superman's powers have been transferred to a guy who uses them to become a superhero for hire, and later a villainess who replicates Supes' powers for eeeeeevil. At the end, Supes Wouldn't Hit a Girl, and is at a total loss as to what to do... and then "Resplendent Man" slugs her.
The title character has no problem fighting female enemies, and has thus far dropped a chandelier on a witch, killed a member of the Sidhe while she's unarmed, made rocks fall on Morgana, blown up a pixie in the form of an elderly woman, electrocuted Nimueh to death with a bolt of lightning, and thrown Morgause into a pillar so hard that she was left disfigured and dying slowly over the course of the following year.
Gaius was also the one who struck the first blow against Morgause. On the other hand, Arthur was reluctant to swordfight with her once he discovered she was a woman.
Uther hits Guinevere around the face when she gives him sass.
Once Upon a Time: Captain Hook has no qualms with hurting women. He ripped out Aurora's heart and backhanded and nearly stabbed Belle with his hook. He physically shoved Emma out of the way to get at Rumplestiltskin. Then, there was "The Outsider" where he shot Belle in the shoulder.
Rumplestiltskin also has no issue with hurting women, if his ripping out his own wife's heart is anything to go by.
Similar to Buffy, none of the monsters in any of the series have any problem attacking the female rangers. This is likely helped by the fact that in many Super Sentai, the Yellow Rangers are male, so a monster hitting a man in Japan is only hitting a girl in America. In one rather infamous example, when the Evil Green Ranger hijacks the Megazord cockpit, he punches Trini across the face so hard she flies across the cockpit.
As an inverse, the male rangers have no problem hitting the female monsters, such as Madame Woe, Lip Syncher, or Dischordia.
They also have few issues with fighting non-monster female antagonists, such as Astronema, Trakeena, and Nadira. In a universe where magic, superpowers, and supernatural fighting ability really level the playing field, this stance is almost required.
In "Sex and Drugs", Drexel. He claims to be adding verisimilitude to the story he feeds Charlie, but his readiness to punch her hard enough in the face to leave a bruise suggests he's willing to do the real thing.
Charlie Matheson gets slugged by a militia soldier and later by a militia recruit in "The Children's Crusade", thereby establishing she must possess a jaw of iron.
Miles Matheson apparently relies on his reputation of lacking any compunction about gender when it comes to killing, since he effectively makes his threats stick in order to get what he wants. "Nobody's Fault But Mine" shows him holding a sword to Julia Neville's throat to make her husband cooperate with him, and "The Longest Day" shows in a flashback that Miles certainly did not hesitate to hit Rachel Matheson and supposedly torture her to death for tricking him.
Rome: Male characters seem to have no problems hitting women. It's notable that an underplayed moment in the pilot episode involves Octavian casually backhanding a slave girl who accidentally bumped him with a chair, showing the attitude to violence in general in the society. Specific incidences include Caesar striking Servillia twice, hard, after she responds to his telling her their affair must end by slapping him repeatedly, and Mark Anthony instantly and heavily backhanding Atia when she slaps him while they have an argument in bed.
Sledgehammer: Inspector Sledge Hammer was always willing to hit or shoot women. In the first episode of "Sledge Hammer!", he shoots a female terrorist, then tells her, "Call me a feminist." Later episodes subverted his willingness to fight women twice: in one first-season episode, he fights a woman who turns out to be a man in disguise, and in a second-season episode, he fights a man who turns out to be a woman in disguise.
Smallville: There are plenty of female Meteor Freaks and metahumans out there, meaning that this trope is in full effect. It would be easier to list the guys who won't hit back, as everyone from Lex to Oliver to Clark is more than willing to. It's never really discussed either; in a world full of superheroes, it's just an occupational hazard.
What's a bit disturbing about Clark's willingness to do this is that he is much stronger than the other males on the show, yet he treats all variations of empowered people (female and male, in fairness) the same, sometimes throwing them and punching them much harder than necessary. He even frequently gets shovey and aggressive towards Tess, who is 100% human with no abilities. (In one episode getting pissed enough at her to Neck Lift her a good foot and a half off of the ground without any thought for the fact that doing so could easily kill her, especially when he's blinded by anger.)
Stargate SG-1: Played for Laughs in the episode "Prometheus Unbound." Vala expresses surprise that Daniel hit her during a fight she started and he replies, with understandable annoyance, "You hit ME!"
Played much more seriously in Line in the Sand when Vala is captured by her former husband (and The Dragon to the Big Bad), Tomin. Tomin is ordered to instruct Vala in the teachings of Origin as a punishment for allowing her to deceive him into marriage. When Tomin tries to give Vala sermons, she talks over him, pointing out all of the horrible things he's done (mostly mass murder) in the name of the Ori and finally shouting "The Ori are not gods!" Tomin snaps and slaps her, though he quickly shows remorse.
Strike Back: Stonebridge has no problems shooting Jessica Kohl (who, to be fair, has no problems shooting Stonebridge). As a general rule, nobody has any problems with shooting women, particularly if the women are shooting at them.
Special mention is deserved by the time that Dean slapped a female demon across the face, twice, just to prove his theory that he was being protected by a higher power. Unlike most of the examples on this page, it wasn't at all self-defense.
The Twilight Zone: In the episode "Two," the man gets into a fistfight with an enemy soldier, who happens to be a woman. He knocks her out cold.
Twin Peaks: Agent Cooper isn't opposed to taking out a woman if she poses a threat. At one point he forced a woman to show him the way to a hostage and then knocked her out cold after she attempted to attack him with a knife.
Seen here. This, however, was exceedingly rare, as usually female villains and lackeys would either go into custody without resistance or be dealt with by several of the female Rangers.
While Walker was (almost) always a gentleman and never struck a woman, this trope was ignored fully by the male villains, who regularly struck women and had no qualms about putting their lives in severe danger. (In one episode, a brute smacks an elderly woman across the face after she warns that God will deal with him for his crimes.)
The Wild Wild West: In the opening credits, James West decks a woman who was about to stab him in the back (in said opening credits he knocked out one enemy and shot another, so this is still a step down on violence). This is a change from the season one opening credits, where he's such a good kisser that she renounces stabbing him. It should be noted that in the series itself the only time Jim actually did hit a woman was in "The Night of the Running Death" - and "she" turned out to be a man.