Use the other teams weapons/equipment against them.

M16, or Famas. If they have ether of these their most likely planning mid range fighting, some are very good long range shots also so if someone has one of these and you have a close range weapon, primary or secondary, close range if how you want to take them on.

Sub machine guns, if they have one unless they are very very skilled or very stupid they will use this for close range with very little mid range, if you see someone having it try to fight them at mid to long range if you have a weapon for it and they will try to fight close so lay claymores, they will try to get close to you and fail.

Light machine guns, Mid to long range only, never use one in short range but if the other team has them then make them use it short range if you can

Snipers, if someone has one fight them close up but not to close, watch out for claymores. The sniper has horrible hip fire aim and horrible at sniping close range but is a 1 to 2 hit kill so if your to close they have a good chance of hip fire killing you so keep a small distance but not to much to lose your advantage.

Riot shield, if they are smart they will have a throwing knife and kill you but not everyone is smart like that, it takes them 2 pushes of the shield to kill you, don't let them get a chance to do that, if they will chase you then run away they may switch to their gun and try to shoot but if you turn while their switching you have the advantage, also its very easy to jump behind them and knife them, also explosives thrown behind them will easily kill them. And finally teamwork, if you and a friend are on opposites of him he cant block both of you.

Machine pistols, shotguns and handguns are meant for close range, right them mid to long range.

Launchers, they have little defense most explode on impact so get close incase they do hit you they die to.

Claymores, if they have it layed set it off and take an alternate route to get to them they will assume your coming where the claymore was at. This also works with c4 if its layed and it works better with ninja pro.

Tactical insertion, most people stand in front waiting, don't ether lay down or move off to the side and face it, double kills can be easy.

Flash grenades or stun, Stay behind cover enough to where its hard to be shot and a stun or flash will barely hit you, they will assume if they hit you knowing where you were at it would be a full hit and you cant see or do anything, but if it only just hit you then you can easily have the advantage since they think your fully flashed or stunned and they are not behind cover and you are.

Thats all for not on how to use their classes against them.