Smart Bomb (item)
From the Super Mario Wiki
The Smart Bomb is an item found in all five Star Fox games, and appears in Super Smash Bros. Brawl. When the item is thrown, it will explode on the spot, damaging any players nearby. However, the shockwave from the explosion expands after being detonated, and can damage the user, if they're close enough.
On occasion, the Smart Bomb will fail to explode, and will simply lie on the ground until, finally, it explodes unexpectedly. Unlike in the actual Star Fox games, the Smart Bomb does not possess the ability to home into the opponent in Super Smash Bros. Brawl.
It is possible to get out of the explosion after the player is caught in it. To do this the player must repeatedly move the control stick in the direction closest to the edge of the blast.
 Trophy Information from Super Smash Bros. Brawl