Call of Duty involves running around a prying to god you don't get shot with a sniper rifle or you react faster then the other guy. A few grenades here and there but no real variation, campaign is good though.
Battlefield is much more realistic, YOU have the POWER to win MATCHES. Battlefiend involves tanks, choppers, APCs, and jeeps (not to mention the jets).
It's up to everyone on the team to win matches, from the elites, to the noobs, it doesn't matter if they're a noob, each person has the power to win matches.
You need a ride, call for a ride. Need ammo? Call for ammo. Need a medic, call for a medic. See a tank, spot it so your team knows where it its. See an undefended objective, capture it and take off some pressure from the rest of your team, possibly winning you the game.