There's a Sunday strip in which Calvin and Hobbes are about to go sledding down a hill, but Hobbes jumps off at the last moment. Then the view remains centred on him and we only get to see a hint of how spectacularly Calvin's ride goes (and fails) by the look of Hobbes's reactions.
The year is 1968. The New York Jets are beating the Oakland Raiders 32 to 29 with 65 seconds left in a critical late-season game. Fans across the country are on the edge of their seats. And NBC cuts the game off to start showing Heidi, a children's movie. And then Oakland scores two touchdowns in the time left, beating the Jets 43 to 32. Executives tried to preempt this, but they couldn't reach operations. No one on the East coast got to see Oakland's comeback. People were rather put out. This has been ranked as the fifth worst television blunder of all time and it will never happen again.
In 2007, Bitter rivals Buffalo and Ottawa were meeting in the NHL playoffs. The game, went into overtime as both goalies were red hot that day. But oops! the game was on NBC, which still hadn't learned its lesson. Overtime was shunted to Versus, an upstart cable channel which few providers carried, in favor of an hour of pre-race coverage of The Preakness Stakes.
2010, July, a hot summer afternoon. England's first match in the World Cup. Expectations are high. All around the country fans gather in pubs, homes and at parties. Three minutes of tense action goes by. The crowd are on the edge of their seats, England has the ball and are soaring upfield as if unopposed. Sky TV cuts out. Two minutes later it cuts back in to the action. The score? 1-0.
During the Evo 2010 Super Street Fighter IV grand final match, the online stream, being watched by over 27,000 people at the time, went out. During the final moments of the match.
For many sports, we have precious little footage of the great players of the era before television became widespread.
Comes up quite a lot to cover unstageable events- sometimes, these days, with the actors facing straight at the audience as if it's happening on the fourth wall.
Was standard for Ancient Greek theatre that everything that actually happened was offstage and characters only appeared to talk about it- it doesn't seem to have been until quite recently that it occurred to dramatists that people might like to actually see this stuff happen
Was therefore also done like this in the early days of Opera, as the whole genre was initially heavily influenced by Greek theatre
8-Bit Theater features this as a fundamental part of the humor of the comic. Most of the promised epic battle scenes (a) don't happen at all; (b) are resolved with a completely mundane anticlimax; (c) get resolved off-panel, frequently by a different character or characters. This includes the defeat of the Final Boss.
"Okay, we were going to dedicate a full Sunday comic to the epic battle, but it's Bun-Bun against a turkey!Come on people!
MeatShield provided the page image as a lampshade to the trope.
Played with again, The ninth issue of Insonicnia is, basically, a standoff between Sonic and Shadow before they start fighting. The tenth issue is missing/broken. The eleventh issue is pretty much nothing but the characters talking about how awesome the fight was... oh, and shadow being convinced to move into the house.
A Running Gag in Basic Instructions is the viewer never gets to see any of superhero Rocket Hat's epic, well, superheroism, just awed after-the-fact descriptions. And then there's this comic, which is one of the most literal examples of this trope ever.
The battle between Mell and Dr. Narbon in Narbonic during the story "Battle for the Lost Diamond Mines of Brazil". Lampshaded to hell and back when Mell comments not only on how awesome it was, but how "hard to draw" it would have been.
Also Eridan's rampage in the Land of Wrath and Angels. The Angels were supposedly unkillable, but Eridan managed to do it through a full minute of sustained fire from Ahab's Crosshairs. He killed so many they started attacking on sight, so he wiped out the whole race.
T-Rex: Time to go on a wacky adventure, which would be quite amazing to an imaginary third party with the ability to see my actions rendered as a continuous narrative! Narrator: LATER: T-Rex: Whew!! Kick ass!
Whatever it was Bluey did with the giant robot in Dragon Tails, it was awesome enough to make Enigma admit that it was pretty awesome.
A knife fight at a Halloween party between a man dressed as Snake-Eyes and a homicidal, Matrix-styling penguin is only related the morning after in thisLost In Confusion strip.
Whateley Universe: in the combat finals for the end of fall 2006 term at Whateley Academy, the authors have showed us over a dozen combat finals ranging from awesome to hysterical to embarrassing. But every character keeps talking about Chaka's unbelievably awesome combat final against three superpowered opponents, in a disaster scenario with a tornado and earthquakes. It wasn't shown, and Word of God says it never will be.
The Homestar Runner cartoon "Weclome Back"[sic] had Strong Bad talking about checking an e-mail in mid-air. Unfortunately, he pulled the "mash stop when you think you're mashing record and mash record when you think you're mashing stop" routine, so all we get is footage of Strong Bad in an airplane talking about how excited he is, and then footage of Strong Bad talking about how incredible the whole thing was, mentioning that they met various celebrities and apparently encountered a narwal. Of course, this being Strong Bad, he might have exaggerated it.
The final episode of Red vs. Blue Season 9 has Caboose recounting their daring rescue operation. None of it is shown due to the perspective of the narrator.
In Das Bo Schitt's Computer Quest  (A side-action Gmod animation explaining why the Gmod Idiot Box Episode 10 hadn't been released yet.), Metrocop #1 and Chuck Norris fight for the final piece of Bo Schitt's brand-new computer: the motherboard. Too bad the scene went missing just as they were going to come to terms, coupled with Peter Griffin's laugh. Doubles as a Crowning Momentof Funny.
Yogscast series Tekkit, episode 2, started out with an exchange by the players about (supposedly sometime between episodes 1 and 2) converting a wooden pickaxe to a banjo, lighting it on fire and playing a solo, and a helicopter.
Episode 36 of Jesse Cox'sLet's Play of Saints Row The Third ends with Jesse stepping away when his pizza arrives while his partner WowCrendor protects him. However, because the videos are streamed from Jesse's point of view, the final five and a half minutes consist of Jesse's character just standing there while Crendor runs back and forth reacting out loud to whatever he's shooting at. The only action we see are the rare moments when Crendor happens to kill something in front of Jesse. Fortunately, Crendor's reactions and the insertion of Yakety Sax turn the Offscreen Moment of Awesome into a Crowning Moment of Funny.
WowCrendor: How long does it take to get a pizza? How long?! Aahh!! The car set me on fire!
In Worm, the Siberian is The Juggernaut and a well-known Hero Killer, to the point that the Protectorate actually avoids engaging her because they've never been able to make any headway. After the Undersiders discover and publicize her weakness, however, Dragon hunts her controller down and kills him offscreen.
Later, there's Heartbreaker, who throughout the entire story has been built up as a scary background villain, a mind-controller who can permanently force his victims to fall in love with him and uses this power to build up an entire family of parahumans. At some point during the Time Skip, Imp-Grue's kid sister-murdered him.
Golem got one when he fought at least ten members of the Slaughterhouse Nine. And apparently won.
Ultra Fast Pony, being an abridged series, will sometimes leave action-packed scenes on the cutting room floor because of the time limit, or for the sake of changing the plot from the original. So, in "Ponynet Fight!" the characters run into a vicious hydra, but their escape is replaced with a "14 hours later..." transition card. And "How to Control Freaks" shows Twilight Sparkle breaking Discord's mind control over most of her friends, but skips over Rainbow Dash. There's even a Lampshade Hanging via subtitle: "Rainbow Dash normalized off-screen."
In the promo for Season 3 of Epic Rap Battles of History, Adolf Hitler kills a Rancor with a regular Luger pistol. All we see is him picking up the Luger, the screen going black, shortly followed by a gunshot.
Heirophant Green and Silver Chariot beat Lovers offscreen during the Lovers arc in Vaguely Recalling Jo Jo. Joseph mentions that involved many difficult battles.
In RWBY, Jaune Arc managed to catch a bunch of Rapier Wasps and put them in a box without getting stung.
Ever had a time where you've missed out on going to a party, either through choice or because you've not been invited, only to see all your friends post pictures of themselves grinning, and saying how awesome it was?
This trope can be expected to happen for various reasons. Statistically, lightning strikes the Earth 100 times a second, but since our scope of vision is so small, we may only witness one lightning storm in a year. Similarly, even though our field of knowledge is vastly expanded by TV, there are far more awesome things which will never make it to our eyes.
Also, due to Stage Fright, a person might be able to perform a stunt when alone, but as soon as they're trying to perform to an audience, they might feel unable to do it. Thus, the audience will never see the awesome stunt they were trying to perform.
This is especially true when it involves a pet: "You should see this really great trick my dog can do!" is usually the beginning of a wasted afternoon.