A riot shield is fine as long as the folks you're facing off against are throwing pretend rocks or pretend Molotov cocktails.
If they're shooting at you with firearms it's useless.
You might as well tell everyone your fairy godmother cast a magic spell on you with some pixie dust and you're now immune to bullets till midnight when you have to jump back into your pumpkin carriage.
For the heavier ballistic shields they will stop pistol/SMG/Shotgun. If you want to stop rifle bullets it's going to be so heavy it's on wheels.
Airsoft, where nothing is hurt but feelings.