The second-year Raiders coach has been clear from the outset -- lose your composure in practice and it may be lost during a game. Not to mention the potential for injury.
Fighting, in Del Rio's mind, is a lose-lose situation from a coach who has his mind set on winning.
The Raiders have skirmished more than Del Rio would like, but a couple of bouts between guard Kelechi Osemele, a big-ticket free agent signed in the off-season, and Mario Edwards Jr., a second-round draft pick last year, particularly rubbed the coach the wrong way.
Osemele arrived with the reputation of having a nasty streak and was paid big-money for it. Edwards was a second-round draft pick who played well as a rookie and is being counted upon for big things in his second year.
So it wasn't as if two fringe players were flailing away, and it wasn't as if the coaching staff was worried about Week 1 as they threw punches.
As for Osemele vs. Edwards, that was another matter. With the Raiders, gone are the days where coaches look at each other with a knowing smile as teammates get after it against each other, thus elevating the intensity of the session.
Osemele and Edwards were ejected from practice, and Edwards missed the following day with a hand injury.
The day after the two squared off, Del Rio addressed it to the press before anyone had a chance to ask.
"I didn't think they were prepared to do the things we needed to do to help our team be able to work," Del Rio said. "They were both talked to and understand that's not how we do things, not what we're looking for. We basically handled it and put it to rest."
Del Rio said the combatants were none the worse for wear.
"They're going to be fine," Del Rio said. "You can have unfortunate things happen when guys go at it like that, so we're grateful that nothing came of it."
In the end, Del Rio thinks the entire team benefitted from Osemele vs. Edwards.
"We learned a big-time lesson on how important it is to take care of each other and be good teammates and still challenge each other and be respectful," Del Rio said.
"It's a good grind. It's the last stretch we'll have like this before we get into game weeks."
Quarterback Derek Carr likes the intensity, but only to a point.
"If that stuff happens during the game, it's a penalty, an ejection," Carr said. "We can't lose one person ... plus we don't want to hurt anybody.
"There's a fine line when you get professional athletes out there."