Have you been in a game and there is always this one person with a riot shield?
I personally hate this so much so i made a guide on how to kill them!

1). you can use tube/RPG/AT4/ and blow the wall behind them or the floor next to them. Nades/claymore also do the job

2). Stun Grenades - These will stun the Riot shielder, if you THROW THEM BEHIND HIM. If the Riot shield is pointing at the stun grenade it won't work, so ensure you see the stun hitmarker before you continue. After stunning them you can move round the side of them for the kill in any way you feel necessary.

3). Run the shielder round for a bit until you can find a team-mate to help. Even those you can't communicate with will never turn down a free waiting kill in front of them. One of you can move round the front as the other kills from behind, resulting in a quick takedown.

4). Hope your Pave Low/Harrier?Attack Helicopter/ airstrike hits the shield guy.

5). Sometimes if you get lucky i will use a shotgun i prefer the aa-12 and shoot at there feet and half of the time it kills them

6). Also my favorite setup is to get them near some explosive barrels or something like thatand just shoot the barrel behind them.

Hope this helps and go kill that one annoying riot shielder.