Yes, he is saying "Bite me!"
How do I know? I'm deaf, and I read lips very, very well, thank you.
There is no way on God's Green Earth that Rivers was saying, "Atta baby!" His eyes were flaring, his face was contorted, even a bit reddened from the effort, and the venom flowing forth from those lips was unmistakable. These were shouts that were meant to be heard and meant to belittle.
He was NOT congratulating or encouraging a teammate. The recipient of his invective was across the field, and he apparently had no desire to engage in this type of conversation face-to-face.
Even the sportscasters, and later some national writers, wondered where Rivers, who has virtually nothing on his resume, got the balls to engage in behavior like that.
Just like most of the other guys here on PatsFan.com, both my wife and I think this guy is an azzhole, and can't wait for the Pats to give him his proper comeuppance.
What we'd really like to see is, as the game is drawing to a close, and the Chargers are getting shellacked, Mike Vrabel comes in and jars his head lose on a very enthusiastic sack, and as he's getting up, looks at Mr. Rivers , and yells out, "Hey! Bite me!"
Won't happen, tho, because the Pats are a class organization, and don't engage in behavior like that.
Rather, they carry themselves as Champions!