He led with the crown of his helmet. In the past, that was known as spearing. It has been in the rules since the ‘70s, but enforcement and penalties have increased in recent years.
Yes, and he not only led with the crown of his helmet, he deliberately lowered his head just before the impact to drive the crown of his helmet into Field's ribs. If you were making a demo tape to train refs on the definition of spearing, that would be a perfect example. Back in the "good old days" (?) of pre-civilized football, that was the kind of thing players did deliberately to try to knock opponents out of the game. That's why, as you note, it was outlawed.