Well i may need help from someone who knows better how to work with vector stuff.
Basic idea: Hook player_hurt event in pre-hook mode, get attacker's weapon and check if its "tank_claw", start 0.05 timer for victim, inside timer check if there are survivors neraby, if found survivors start staggering for them, stop timer if victim landed on ground.
The only REAL problem here is how to force survivors stugger. Should find a way to do this first.