That cornerback may have been up to something other than just running as fast downfield as he could, but how anyone could possibly know that he was planning to break up a passing play is a mystery.
Even if he was doing what you say, the officers actions would still be wrong after they took him down.
What did they do wrong, exactly?
Do you think that no criminal would ever stoop to something so low as to fake distress and play possum?
They took him down, they checked his pulse when he went out, they got him on an ambulance.
A cornerback?
He was doing something else because you just know it in your heart of hearts?
Strong evidence, not that it matters.