Serious foul play. Endangers the safety of an opponent.The Laws of the Game don't quite agree with you....
Reckless is when a player acts with disregard to the danger to, or consequences for, an opponent and must be cautioned.
Using excessive force is when a player exceeds the necessary use of force and/or endangers the safety of an opponent and must be sent off.
Of course Emerson Royal got sent off at Arsenal for a much less serious offence.
Again the issue is that the Laws are written very badly and subject to too much interpretation. The definition of using excessive force is essentially using excessive force and/or endangering but reckless is a lesser offence. That's so unclear it's not surprising it's applied inconsistently

