49ers HC Kyle Shanahan upset over fights during practices

The San Francisco 49ers have endured a physical training camp ahead of their preseason opener versus the Green Bay Packers at Levi's Stadium next Friday. 

Specifically, wide receiver Brandon Aiyuk and linebacker Fred Warner were "ready to throw hands" during Tuesday's session after receiver Marcus Johnson landed in the concussion protocol following a late hit delivered by Warner. 

Per Nick Wagoner of ESPN, head coach Kyle Shanahan had to halt practice on multiple occasions on Tuesday because of fights among players. Shanahan spoke with reporters on Friday and used the occasion to remind those in his locker room that there is a difference between showing toughness and partaking in actions that could get one penalized during a game or even tossed from a contest. 

"I want everyone challenging each other," Shanahan explained. "I don't care how much crap each other talks; I don't care how close they get to fighting. They can do whatever they want to get themselves to be as intense as they want and bring the best out of each other, which happens a lot that way. And it's the same on the field.

"But once you throw a punch, you get ejected or you get a penalty, and we pride ourselves on, I want people to be irritants, I want people to get as close as they can to all that stuff. I want people to get right on the line where they're about to black out, but you can't black out on the football field or you cost your team."

Shanahan noted that Tuesday's incident involving Aiyuk and Warner is an example of something that's unacceptable, largely because potential brawls can lead to injuries such as broken hands if punches are thrown by players wearing helmets. 

"I think our team is pretty tough," Shanahan added. "I think we're pretty physical. I think if most probably voted on who would be the most physical team on tape last year, I think we'd win most of that, and we didn't get in one fight last year. So, I don't think that totally pertains to toughness."