The call?

[Mike L]

Originally Posted by Ch1town

Team A linesman has his mouthpiece swinging during their 2nd down running play. Flag is thrown, play continues & Team B recovers the fumble.

What do you have (Fed)?

Like others have said, this foul needs to be prevented from even happening, but failing that it must be called before the snap. If the snap has already happened, then you need to waive the flag off because it now appears you don't know if it came out before (which is a foul) or after the snap (which is not), and if you are not 100% sure about the foul you shouldn't be throwing your flag.
But if you insist on enforcing this, it's B's ball after a decline, unless of course they don't want the ball.

[HLin NC]

I'm with the officials, not Team A

I believe the case book says that IF you see a player intentionally not using required equipment during the down-such as spitting out his mouthpiece or unbuckling his chinstrap it is a foul. If you do NOT see the act, then you are to assume the dis-use (?) resulted from game action and is not a foul.

If you catch it during the dead ball period, you should try to get the player to correct it and if not, flag and kill it for Failing to Wear required Equipment, which is considered delay of the game, I believe.