There was a $1500 bonus for "cart off" hits.
That is intent to injure...and it doesn't matter if it applies to a specific player.
It's perfectly kosher for the players (or a subset thereof: special teams, defense, etc...) to offer up internal incentives for key plays: sacks, ints, special teams plays inside the 10. That is the players generating competition amongst themselves for legal objectives. The league might frown on it, but it won't/can't stop it or articulate an exact rule this violates because it isn't team (read: franchise/league) sanctioned.
The problem here is twofold:
1) Williams (team/league rep) apparently endorsed this injury for pay incentive...to the extent of providing his own (team?) funds to pay the incentives; and
2) Incentives, regardless of the trigger, paid by the franchise/team violate the cap rules.