Recently i have found a great riot shield class and it is extremely useful so try it out
In this class you should have
Primary:Riot Shield (obiously)
Secondary: aa-12 (extended mag)
equipment-C4
and stuns
Perks-
scavenger
Danger close
Commando

How this class works-
when facing a Riot shielder most dont expect them to switch to their secondary and try to rush and this is where the aa-12 comes in as it is the second best close range shotgun (The reason u would use this is because of ammo clip size, rate of fire and damage)
Then the c4 comes in handy if u are using stuns because there are also kids who run away from riot shielders. So u stun them and throw ur c4 and with dangerclose ur more likely to kill them. Now comes scavenger, once you have killed an enemy you pick up their ammo pack and repeat the process

More Riot shield tips:
-Never run from enemies (ur back is exposed!)
-Never charge unless you have to(sometimes kids like to knife right through ur riot shield)
-Dont always rely on ur throwing knife as they are not very accurate (try to use your secondary especially if it is a machine pistol becuse they are good for close range and medium
-alway try to stun ur enemy before trying to rush ( they are less likely to fight back)

Hope this helped now get out there and go try hard with ur Riot shield