When announcing the penalty, the ref said Coop "went out of bounds voluntarily." I've seen some argue that Cooper should have been eligible because he was "forced out." I've also seen others say that even though he was forced out, Cooper didn't 'immediately' return to the field of play. I don't think either of those explanations are relevant.
From RULE 8, SECTION 1 FORWARD PASS, ARTICLE 6. INELIGIBLE RECEIVERS (added emphasis):
(d) An eligible receiver who has been out of bounds prior to or during a pass, even if he has re-established himself inbounds with both feet or with any part of his body other than his hands.
Exception: If an eligible receiver is forced out of bounds by a foul by a defender, including illegal contact, defensive holding, or defensive pass interference, provided he attempts to return inbounds immediately, he will become eligible to legally touch the pass (without prior touching by another eligible receiver or defender) as soon as he re-establishes himself inbounds with both feet or with any part of his body other than his hands. See Article 8, Note 3.
Cooper was not forced out of bounds by a foul (no flag was thrown on Trufant), so the exception did not apply. Could Trufant's push have been called a foul? No.
From RULE 8, SECTION 4 LEGAL AND ILLEGAL CONTACT WITH ELIGIBLE RECEIVERS, ARTICLE 3. ILLEGAL CONTACT BEYOND FIVE-YARD ZONE (added emphasis):
Beyond the five-yard zone, if the player who receives the snap remains in the pocket with the ball, a defender cannot initiate contact with a receiver who is attempting to evade him.
At the point in time when Cooper was pushed out, Carr was out of the pocket. The push was therefore not illegal contact.
e: Also of note, new this year, an eligible receiver illegally touching a forward pass after being out of bounds and reestablishing himself inbounds was changed from a 5 yard penalty to a loss of down. So had this happened last year, it would have resulted in 3rd and 7, rather than 4th and 2.
