I'm assuming you're talking about the MP game. This is a finishing move performed while one is in a saber lock. I think the other person hit their secondary fire (throw lightsaber) while in the middle of the lock. There are a couple ways to defend against this in single player but since I don't play much MP I dunno if this is applicable in MP. Anyway, here goes: 1) Push out of the saber lock before the other person gets tempted to use this method. 2) Try and win the lock before he/she uses the move. Method 1 breaks both of you out of the lock, neither winning but hey, look on the bright side, you're not dead in one move. Method 2 is a no-brainer but I thought I'd include it. As far as not being hit by this move, there is no such tactic.
"Size matters not."-Yoda
"There is no emotion; there is peace. There is no ignorance; there is knowledge. There is no passion; there is serenity. There is no death; there is the Force"-the Jedi Code