The rookie head coach was displeased after a soft penalty saw his side go behind, although it later recovered to earn a point at home.
Although RSL later came back to claim a draw, the visiting side was awarded a spot kick in the 73rd minute. Defender Nat Botchers was judged to have fouled Darren Mattocks in the penalty area, although replays showed the defender won the ball cleanly.
"It’s not a PK," Cassar told reporters after the match. "It’s 100 percent not a PK – I just watched it again. I wish the referee would, you know, be positive [about a call like that]. I went up to him afterwards and asked him, 'Are you sure about that call?’ He said ‘pretty sure.’ It’s a PK in the box – you need to be sure. You can’t be ‘almost right’ about those types of calls.
"Maybe in the middle of the field, you can get away with that, but not a PK. It changes the game, changes the momentum. I was really not pleased with that call."
The draw against Vancouver means Real Salt Lake has won just one of its last eight matches.