On network TV, when sporting events run longer than the scheduled time, the following program (usually syndicated) is pre-empted and the game remains on air until it is finished. In other instances, network programming will be delayed until the game ends, such as when Fox began showing football on Sunday afternoons, delaying The Simpsons by as much as 15 minutes and shredding the later seasons of King of the Hill, which was usually joined in progress after the football games ended, usually at half past the hour.
This practice goes back to a 1968 American Football League game between the New York Jets and Oakland Raiders that aired on NBC, now known as the Heidi Game. With the Jets up 32-29, the last 65 seconds of the game were cut off in the eastern United States when the scheduled three-hour timeslot ended and a made-for-TV movie adaptation of Heidi went to air; NBC executives decided to allow the game to finish, but were unable to tell network control about it because their phone lines were jammed up by viewers' opines over the situation. In the unaired minute, the Raiders scored two touchdowns and won the game. NBC was widely criticized for cutting away from the game (flashing the final score showing that the Raiders won in the middle of a rather important scene only served to piss off both audiences), and made a public apology.
Now, since there is considerable blowback from non-sports fans (and sports fans who enjoy other shows) about joining "your regularly scheduled programming" already in progress, many times cutting important parts of a show (on a show such as CSI or NCIS, the majority of the plot will be set up within five minutes), networks will often block out extra time for this, making the remainder a post-game talk show of indeterminate length. That way, if a broadcast goes long, the game will only eat into the time allotted for the post-game, which will often only last to round out the hour, and THEN go into the rest of the TV schedule. This is Fox's current strategy, with a post-game show called The OT filling out the hour, killing an hour that for 14 years was Fox's own version of a Death Slot. Because of this, it's very rare (like when the Rams and 49ers played to a tie in November 2012) that Fox has to delay their Sunday programming at all.
Because of the popularity of 60 Minutes, CBS will usually delay the start of that show until every NFL game to which it has the rights is over, then air it in its entirety, delaying the network's entire primetime schedule accordingly. This infuriates fans of the network's Sunday shows (especially those that use DVRs) as they cannot predict when their favorite show will actually start (especially if CBS switches to another game for "bonus coverage", and that game goes into overtime). In September 2012, CBS decided to just bump up the lineup a half-hour on game nights (concurrent with the NFL moving its late-afternoon doubleheader games from 4:15 to 4:25 ET, effectively forcing the issue), though the games still leech into the second half-hour and cause delays, to the point that CBS has to maintain an Twitter/app service that sends out delay alerts; sometimes this has the side effect of killing the 10pm show for that night, a fate that befell a new CSI episode which was rescheduled three times in October and November 2014 due to long-running games.
As the quote at the beginning indicates, this is not just an American phenomenon. A variant on this significantly heightened "geek vs. jock" hostility in UK popular culture in the 1990s, due to The BBC's tendency to show imported American SF/fantasy series (such as Buffy the Vampire Slayer and various Star Trek shows) on BBC2 on weekday teatimes and cancel them altogether whenever some big sporting event happened.
On networks devoted to sports programming, there have been cases of sports preempting other sports. A notable example is ESPN's infamous 2007-14 NASCAR coverage, in which college sports was given priority, and race broadcasts were cut short or relocated; one of the most infamous examples was the 2014 Bank of America 500 (the last race aired on ABC before the new television contract with NBC went into effect the next year) had its first 25 laps preempted due to a college football game between TCU and Baylor running late; the race was supposedly relocated to ESPNEWS, where it was also preempted because of a preseason NBA game in Brazil going into overtime; the race was said to be on WatchESPN.com (which it wasn't), and RaceBuddy (a service on NASCAR's website with multiple camera angles) was not provided because the race wasn't on a cable network; the only way anyone could follow the start was through the PRN radio broadcast, or via the NASCAR mobile app. Coverage was joined at a scheduled competition caution on lap 25, at which point an apology was immediately issued by lead broadcaster Allen Bestwick and a recap of the first 25 laps shown. To add insult to injury, several ABC affiliates actually decided the race wasn't important and aired local news instead. NASCAR itself was also unhappy with the move, and apologized to irate fans.
Although the trope is primarily associated with sporting events, there can be other causes for pre-emptions of this nature, including awards shows (which notoriously overrun) and scheduled political broadcasts such as the State of the Union address. Often networks will address overruns by either pre-empting an entire night's schedule and filling the remaining time with programming such as Barbara Walters' post-Oscars interview specials, or scheduling expendable reruns.