Tony Smith questioned the decision to sin-bin Ryan Brierley in Hull KR’s defeat to Castleford.
The halfback was shown a yellow card for a collision with Grant Millington early in the second-half as a kick went towards the in-goal.
Castleford made most of the man advantage, with Danny Richardson scoring eight points in that time to put the Tigers ahead for the first time.
“I thought the sin-binning was harsh,” said Smith.
“I didn’t think it was a penalty. Two players are allowed to compete for the ball and push each other with their shoulders, not with their hands, but with their shoulders. That’s what it was, for me but obviously Chris (Kendall) saw it differently.
“I’m going to have to go watch it again and again and again and again to see if they’ve changed the rule. Maybe that rule has been changed, I could be well and truly in the wrong.
“It was a big moment. We can’t afford to have people off the park.”
