A bug is an oversight in computer programming that causes behavior other than what was expected of the code. Most bugs in fighting games are annoying, unintentional glitches that one has to go far out of one’s way to witness, and aren’t even that cool to see. Some bugs can be isolated and used to one’s advantage regularly – bug exploitation can add a new level to play, or take away from play entirely.
Bugs are simply unnoticed or unaddressed by developers before games are shipped. Because updating is a genuine hassle on any platform that doesn’t have regular online access (and free or cheap support from the developer), no matter how awful the bug is (even going so far as to fry out the game’s circuitry in the worst cases), there are plenty of bugs that are left as-is in the arcades.
Furthermore, some developers in the past have failed to fix issues, explaining things away with “workarounds” and trying to hide problems with retcons (and it will happen again in the future, no doubt).
It has been noted that miscounted frames and such causing infinite combos and death combos (among other things) are not included in the description so far, but in a strict sense, miscalculations (human error rather than programming that is off the mark) count as “bugs” from a player perspective.
Some characters are so buggy that they can actually destroy the balance of the game, and can go so far as to ruin the entire game (Pet Shop in JoJo or Foxy in KOF 2001, for example, can be used to this effect).
Especially feared in most games, the dreaded freeze exerts its cold influence. May Lee’s glitch mode in KOF 2001 and Rei’s “bug shōryū” in Hokuto no Ken are two of many examples that are known to reliably cause games to lock up.
A noted example of bugs going into widespread use is the “roll cancel” in Capcom vs. SNK 2. Regardless of its difficulty and Capcom’s subsequent (but not full-blast) efforts to squash the bug, it has characterized (if not enhanced) high-level play of the game ever since it was discovered.