Napoli took a couple of steps toward McCullers while yelling at him, and McCullers did the same. Astros catcher Brian McCann quickly got in Napoli's face, and, after a few seconds, players from both benches began spilling onto the field.
Players from both teams did some pushing and shoving, and George Springer held back McCullers as he continued to bark at Napoli. Order was restored after a couple of minutes, and both teams received warnings before play resumed and McCullers struck out Napoli.
The Astros went on to win 6-2.
McCullers denied intentionally throwing behind Napoli.
"I was just trying to go in; it got away," McCullers said.
Napoli saw things differently.
"I've been in the game a long time," Napoli said. "I understand how things work. Two of their guys get hit, but all he has to do is put it in my hip and I run down to first base. No one likes 95 [mph] behind their back."
The bad blood between these in-state rivals was evident even before the first pitch Monday when the Rangers printed out a tweet by Houston third baseman Alex Bregman and posted it on a board in their clubhouse. The tweet was mocked not only for its content -- saying he wanted to beat the Rangers -- but also for the fact that Bregman misspelled the word "operation" by writing "opperation."
"I made a rookie mistake," Bregman said. "I shouldn't have tweeted that out. It was more of just trying to fire up our team, and I shouldn't have put it on social media at all ... poorly worded. Obviously I misspelled a word, another rookie mistake there."
The 18 games left in this in-state rivalry should be rather interesting.
"You don't want anybody to get hurt, but you want high-emotion baseball," Houston manager A.J. Hinch said. "This is fun for us to play with a little bit of edge. We'll see them [Tuesday]. We'll see them 18 more times. Obviously, it should be a fun summer."
The Associated Press contributed to this report.