The Engie was probably doing some Tony Stark shit, building these weapons and teleporters, and The Administrator heard about him form his grandfathers work, or some convention, or the army or some shit. 

I'll bet the Heavy was a Russian Legend. And The scout probably had a criminal record, or he was just really fucking fast, doing track and stunts and shit. Come to think of it, how would the Scout get sought out? His abillity to jump twice?

>We need the deadliest killers around. We've got a war-crazy rocket expert. A Russian who's killed people with his bear hands. 
>What about this kid from Boston? He can jump twice!
>get him on the fucking phone