Penalty for Sandbagging

I am playing a game of chess in a tournament.  The first game against this player, his rating was around 1500, mine at about 1680.  He pulled off an upset after I played poorly.  So my rating went down some and his rating went up some.  Great.  The second game, his rating started at about 1550, mine at about 1660, and as the game has progressed, his rating has dropped dramatically.  Right now, my rating is about 1630, his is about 1100, when literally 10 minutes ago, he was at 1300, and several hours ago, his rating was 1440.  I have a feeling that he is sandbagging just to win back a ton of rating points as he is winning this second tournament game against me, and to kill my rating.  I looked at his history, and he lost 8 games TODAY!!  Several of them looked like either the opening or middlegame, and he RESIGNED AGAINST A 600 AFTER PINNING THE OPPONENT'S QUEEN TO THE KING!!  Could someone please check and make sure that this is legal??  I'm sure that some of his losses and wins were real, but eight losses in ONE DAY!!  That looks so artificial.

Maybe he hacked for something or then deleted his account that same day, but why would he resign cuz of the opening?!

Sandbagging is not easy to prove. Plenty of reasons and excuses why the higher rated player lose. He resigned because of an urgent matters. He blundered or made random moves because of alcohol, drugs, etc.