Neil Warnock left The Hawthorns disappointed as his team were on the wrong end of a couple of decisions after they had led 2-0 courtesy of goals from Brede Hangeland and Mile Jedinak.
The home side came back into the game courtesy of a goal from Victor Anichebe but Julian Speroni was felled by Craig Dawson and had to leave the field of play after the goal. .
Neil said: "It's almost an assault, how one of the four officials can't be in a position to see that. Dawson had smashed him in the face and I am lost for words.
"He's had a two- or three-yard run up and smashed him in the face. No wonder Julian is a bit groggy. He wanted to carry on.
"I can't say anything about the referee or I get fined and I don't want to because I thought he had a cracking game but he had made two or three really bad mistakes."
Earlier in the game before a penalty was given, that was converted by Mile Jedinak, the boss felt his team should have already been awarded a spot kick.
Wilfried Zaha appeared to have been fouled by Dawson but none of the visitors appealed for a penalty but Neil feels it may have been because of how his side had been criticised a week before for their actions.
"You can't win, we had four or five surrounding the referee last week and we were told that was wrong. He (the referee) had a good game but two, maybe three, decisions went against us and it's cost us."