Spring canceling is a technique in Super Smash Bros. Brawl that allows a character to avoid all landing time lag, provided they land on a spring. Whenever a character lands on a spring, that character is immediately sent upwards in an initial jump animation, regardless of the attack they were performing. This works with the item springs, the spring from Sonic's up special move, any spring placed on a map in the stage builder, and even (though this is rarely practical) Mr. Game & Watch's up special move. Spring canceling does not work on the springs on Pictochat.
Spring canceling is the easiest way to avoid any lag from an aerial attack. This becomes especially useful with many characters down A aerials because they can perform them, hit the spring, and continue on with no lag, setting up easy combos. In particular, Kirby will immediately transform out of his Stone upon hitting a spring. Using this, a Kirby player can drop in fast with Stone without any worry of the opponent taking advantage of his transformation time. This also applies to all stall-then-fall aerials.
Also, an immediate short hop second jump can cancel the jump from the spring. If the character fast falls after this, it can allow a player to spring cancel without then going back into the air. Finally, it can work as a mindgame, by cancelling several aerials on the spring, then striking unexpectedly.
Spring canceling is an immediate effect. Therefore, any character that hits the spring will immediately withdraw all of their attack hitboxes. This, coupled with the jump, can make for some unwanted actions if not properly prepared for. Also, all knockback is removed once a character hits the spring. While this can help the character being hit, it can severely disadvantage the opposing player as it can negate even the strongest of moves.