[i_c_b]

Ah, yeah. If you go through the code there, Bryan had to change that file in quite a few places to implement crouch sliding.

Nick Maggoire is an animator. Super nice guy. No inside voice at all. I shared an office with him for a while :) I haven't kept up with him, but after Q4 he left for Valve where he's been ever since, it seems.

That comment strongly suggests to me that Nick did the animations for players crouch sliding. Or, that's my hunch anyway.