Harlequins boss Conor O'Shea was upset over the performance of referee Llyr Apgeraint Roberts after his side's 31-26 win over London Welsh on Sunday.
Although Quins secured a bonus-point from the result, O'Shea was far from happy and accused the match official of several errors.
"I'm unbelievably frustrated, you'd have to go a long way to see worse," he said of Roberts' performance.
"Everything was wrong - it was incredible. The offside line was irrelevant, trailing runners coming back was irrelevant, backing into the maul, not releasing in the tackle - all irrelevant.
"We were 21-6 at half-time but bafflingly the penalty count was against us, how that can be?
"We have a feedback process for the referees but it's not actioned upon and it's very difficult at times."
But despite his criticism of the referee, O'Shea was pleased with his side's showing.
"We played some magnificent running in the first 45 minutes and that's what we should be talking about - our full-back, Ollie Lindsay-Hague, dazzling people with his footwork." he added.
London Welsh head coach Lyn Jones was happy with his team's fightback in the second half.
"At half-time we were staring down the barrel," he said.
"We started the second half well, we were still in there and we needed to get the first score, which we did.
"We had a chance to win but their class and ability shone through in the end. They are a very good side and it's a pity more sides don't play like them.
"We are showing determination and spirit and are good enough to stay in this league."