Tru was the problem. Barron had the Gap and Tru tackled him from behind for no reason whatsoever. that was about the dumbest play I have ever seen Tru make.
Yes but why the hell did Barron have that gap instead of outside contain when there was no DE on outside contain? It is terrible scheme to put a CB into primary outside contain. CB's are secondary outside contain; DEs and LBs play outside contain for a reason -- they are better suited for it and know how to do it against big body blockers, as opposed to a CB.
Go back and look at the defense alignment on that play... a 4-3 shift with the weakside OLB playing 4 yards off the line? On 4th-and-1? NE brought an extra OL on the left side and the Rams took the bait and shifted towards it, leaving absolutely zero LB or DE on the other side line of scrimmage when Hayes slid down outside shade of the *guard*. That left two undersized guys responsible for weak side run responsibility versus the TE, OT and lead back. The Pats could collapse the edge in their sleep. It's almost as if the Rams expected they were subbing in another DE or something (that would have made more sense on 4th-and-1) but that didn't happen.
So yes the players were bad, but this is part of the undersized experiment the Rams run on defense. They expect guys like Barron that can't shed blocks to react & destroy with their speed like a missile into whatever gap they guess, which means giving up plays like this in tradeoff for more stuffs. Tru tried the same penetration (like he does very well on WR screens), but as a CB he doesn't understand that's not the time to do it if you are the only outside contain -- and besides those were real blockers, not WRs.
Basically, the Rams got outcoached and outschemed here. The Pats diagnosed the Rams weakness of undersized defense then used personnel to move the Rams alignment tendency right where they wanted it to put themselves into even further advantage. That's just good football and the type of offensive coordination we haven't seen since Martz?
