House rule question: Grenades and delay

[Targan]

No PC has ever attempted to return an armed grenade in any of my games. My brother's first character in my current campaign threw himself on a grenade booby trap that he was trying disarm when he critically failed his skill check followed by a second failure. His selfless action probably saved the rest of his team's lives.

[jester]

For me the roll determined how many seconds they had, and then I would usualy have a negative modifier, and unless it was a 1, then they'd have to roll verses the GMs roll, he beats my roll he wins, the GM beats him, the grenade wins.