Mental acuity or intelligence in contrast to great power or physical strength. This isn't a case of brains versus brawn—you need both intelligence and physical strength in a situation like this.

slang A way to designate the players on two different teams in a casual sports game in which the teams do not have uniforms. The "skins" are the players who remove their shirts (thus exposing their skin). Come on, guys, we don't have all day—let's just do shirts and skins and start playing!