The NFL has dished out fines to multiple players who criticized the officiating in last weekend's slate of games.
Mayfield was fined for comments he made about officiating after a 32-28 loss to the Seahawks last Sunday. He was asked about a blindside blocking penalty called on Browns wide receiver Jarvis Landry.
"The refs are never an excuse," Mayfield answered. "I will probably get fined for saying this, but it was pretty bad today. The guy is squared up with him, running at him and he is lowering his head into Jarvis. What is [Landry] supposed to do? Avoid him? This is not bullfighting. I don't know. It ticks me off."
Matthews criticized the officiating via Twitter on Monday, one day after the Rams dropped their third straight game, a 20-7 loss to the division-rival 49ers.
"The storyline for the 2019 season continues to be the refs inability to make the accurate and correct calls week in and week out," Matthews tweeted. "Al Riveron continues to blindly side with his refs and the current status quo. Something must change! Zero accountability."
Walker was flagged for unnecessary roughness for a helmet-to-helmet hit on Packers receiver Geronimo Allison in Detroit's 23-22 loss to Green Bay on Monday night. After the game, Walker said the call was "awful."
"I felt like I went for the ball and [it] just so happened we collided, but I was looking for the ball. It was an awful call by them. It is what it is, though," he said.
ESPN's Jake Trotter and Michael Rothstein contributed to this report.