A counter hit (カウンター Kauntaa?) refers to an attack landed when the opponent is in the process of starting up their attack.
Counter hits grant various bonuses depending on the game; in all appearances, they result in longer hitstun and more damage (only during said hit), as well as a slight frame advantage. Some attacks cannot be counterhit out of, due to invincibility in the move's startup frames. Most games have the word "counter" show on the screen when a counter hit is landed.
Street Fighter IV seriesEdit
If a Level 1 Focus Attack, which normally has no effect, strikes an attacking opponent, the counter hit will crumple them. Higher level Focus Attacks do not have this property, and are instead inherently able to crumple any opponent they hit.
If a Level 2 Super Charge is Dash Canceled, the next hit landed will automatically be a counter hit, which can activate counter hit effects of normal attacks that have them (such as crumples, ground bounces, or stumbles)
Street Fighter V seriesEdit
In addition to regular counter hits, Street Fighter V adds a Crush Counter property that functions similarly to crumpling; if a Crush Counter occurs, the opponent is spun around, leaving them in a vulnerable state that grants a large window for follow-up attacks.