Then things went a bit over the line when a hard hit by Dallas cornerback Morris Claiborne on Oakland tight end Mychal Rivera led to a brawl that nearly spilled over into the stands and featured a Raiders fan swinging a helmet at a Cowboys player and cornerback B.W. Webb retaliating with a swing at the fan.
"It's definitely a dangerous situation," Webb said. "I don't know why fans would want to jump on this side of the fence. I don't think they'd like it too much on this side."
A Raiders fan in Oxnard, Calif., posted an Instagram video of the incident, showing the fan take a swing at Webb with a helmet -- and make contact:
But even that brawl and a smaller one on the other field involving Cowboys running back J.C. Copeland and Raiders linebacker Justin Cole couldn't mar the day.
"I don't like the fights. I want to come out and practice football," Raiders coach Dennis Allen said. "We don't have any time for that, and we certainly don't want to get anybody injured in fisticuffs. I thought both teams came out and competed and got a lot of good work in."
CBSSports.com reports that when asked about the incident, Raiders owner Mark Davis said: "Nothing better than Raider fans."
Cowboys owner Jerry Jones praised the enthusiasm and atmosphere of the practice that was watched by 8,326 fans, many of whom lined up early in the morning for the chance to watch.
"It was hard to believe that this was a practice," Jones said.
The practice was more physical than anticipated with players frequently being brought down to the turf despite both coaches saying before it started that they did not want any live tackling.
But after nearly three weeks of practicing against each other, the players were excited for the chance to hit players in another jersey.
That's how the first brawl started. Claiborne felt as if Rivera lowered his shoulder to try to break a tackle so he responded by throwing Rivera to the ground.
That raised the ire of Raiders receiver Greg Little, who came flying in to protect his teammate, leading to the fight on the sideline in front of a boisterous group of Raiders fans.
Players even ran over from the other field to get involved before everything was broken up.
"When I came to the sideline, guys were still talking about it and talking about how it amped them up," Claiborne said. "It should have happened a little earlier in practice and maybe we would have gotten a little more noise out here."
This was a homecoming of sorts for the Raiders, who held training camp at this exact site from 1985-95.
Celebrities such as Magic Johnson and Tommy Lasorda even came out for festivities.
The Raiders had many fans from their time in Los Angeles on hand and officials were extra careful to keep the two teams' supporters on opposite sides of the field.
The Raiders fans seemed to outnumber the Cowboys supporters and there were derogatory chants from both sides and a chant from Raiders fans of "Bring them back! Bring them back!" in hopes of a possible return to Los Angeles.
"It's a reality check for all the new guys who thought they knew what the Raider nation was all about," Raiders fullback Marcel Reece said. "They'd heard the stories and put on the jersey one time for a preseason game, and it's a reality check for them. They have no idea what it is, and they come here to another team's training camp and they out-show their fans."
The teams will hold another joint practice on Wednesday.