Punishment is the act of attacking an opponent while they are vulnerable, usually from using an attack with slow start-up lag at a non-opportune time or having missed an attack with high ending lag. For example, the Falcon Punch is a punishable move since it has long start-up and ending lag; if Captain Falcon uses it against an active and expecting opponent or if the move's target is able to avoid the attack, they have ample time to launch a counterattack. Characters can also be punished if their attack is shielded, such as via shield grabbing or out of shield attacks. An attack that is difficult to punish is usually known as "safe", usually due to having low ending lag and/or large hitboxes that are difficult to get around. A move's power can also make it safer than it appears; some players may choose to avoid the forward smashes of Ike and King Dedede rather than attempt to punish them simply because of the risk involved.
Characters can also be punished if they have used a move that causes helplessness, or they are in a position where their only recovery option is obvious and predictable.