Mystery of why NFL Coach will cover face with clip board during game?

Why do NFL coach's often cover mouth during game with play card or clip board?   I spent a few days with this question and presented it to many radio and television engineers.  "Lip readers hired by opposing teams"  was the popular answer but was it  the  orginal  reason ?  Actually no.   I finally found a printed note  of who was first (NFL Coach) and who shared it on national television.

John Madden (Former NFL player, Coach and Television Sportscaster) told the story on Monday Night Football in 2002 that supposedly explained that EAGLE's  coach Andy Reid started the whole lifting the play sheet to your face when you call the plays. He says that it was  done because the QBs claimed it made it easier to hear the play calls in a loud and windy stadium. The radio systems were very basic two way radios and they were not known for filtering ambient sound.  During telecast's a handful of announcer's began to share rumors of NFL teams hiring lip readers to translate opposing coaches. This practice has never surfaced. Toss this in the rumor pile of when Century Link Field (Former Qwest Field) was pumping crowd noise over PA system?  NY Giants actually filed this complaint vs. Seattle. The NFL had an investiagation and found nothing. We are the loudest stadium in The National Football League.

Seahawks Coach Pete Carroll never has a clip board in his face. Todays Coach/Player radio system is much better and that includes a better  wind sock/noise reduction of the headset mic he wears. Former Seattle Coach Mike Holmgren covered his mouth all the time.

This monring I had this question as the "Payoff at 7:15".  Many true football fans went with the "Lip reader" answer.  Susan of Tacoma was the first to go with the Radio Mic/Reception quality reason.