hey okay its simple
you can cheer in game..
as its there you have the animation
man_cheer
but there is nothing in game to trigger it for humans
you could set your own mission temps to do it but nobody will see it
the server sets the rules
however if you are on a server which has it
for example in scripts
anim_surrender_end (the bit where u finish surrendering)
was replaced with anim_cheer
then you could yourself without any alterations to your game, cheer in game
so yeh you can eaisly write a client side one
but for it to show up on server the server needs to have it
you can if you mod or have your own server easily to a agent_set_animation command to a prop or something
good luck