CHICAGO (AP) — Marcus Stroman is getting used to Major League Baseball’s new pitch clock. And it’s no small deal for the right-hander.

“It’s tough, this pitch clock. It’s a big adjustment,” he said.

Stroman committed baseball’s first regular-season pitch-clock violation in the third inning of the Chicago Cubs’ 4-0 victory over Milwaukee on Thursday on opening day.

Stroman took a long look at rookie Brice Turang leading off second base with no outs and Christian Yelich batting at Wrigley Field. Just as Stroman turned his attention back to Yelich, plate umpire Ron Kulpa called the violation. Kulpa pointed to his wrist in announcing the call, and the automatic ball made it a 2-2 count against Yelich. Stroman didn’t argue.

“You got to be looking at the clock. You’re trying to worry about the pitch. You’re trying to worry about the guys on base. You’re trying to worry about your grip,” Stroman said. “There’s so many things going on now.

“So it definitely adds another layer to the game that’s tough, to be honest with you. It’s definitely not easy to be a pitcher out there and to feel rushed at times.”

Several more violations followed on the first day of regular-season games since MLB introduced a slate of rules changes this season — including a clock for a sport that famously existed for decades without any timers.

Boston Red Sox star slugger Rafael Devers earned an unpleasant spot in the league’s record books as the first batter to strike out via violation. Devers was looking down and kicking debris off his cleats in the eighth inning when Lance Barksdale signaled a violation that resulted in strike three.

“There’s no excuse,” Boston manager Alex Cora said. “They know the rules.”

J.D. Davis of the San Francisco Giants became the first hitter called for a pitch-clock violation in any count during the ninth inning of a game at Yankee Stadium.

Meanwhile in Washington, Atlanta Braves reliever Collin McHugh put his arms out wide after being called for a violation by umpire Dan Bellino in the eighth inning against Washington. That put batter Jeimer Candelario ahead 1-0, and McHugh followed with three more balls — a three-pitch walk, essentially.

“I didn’t even realize it happened, quite honestly,” Atlanta manager Brian Snitker said. “It’s going to happen.”

The opening day rollout was mostly smooth, but a few issues arose in Miami.

In the fifth inning, New York Mets ace Max Scherzer stared down the Marlins’ Bryan De La Cruz until the clock hit zero. De La Cruz began shouting “Ball! Ball! Ball!” — as in, call an automatic ball. But plate umpire Larry Vanover thought the hitter was calling for a timeout. Scherzer escaped without the automatic ball and later induced a popup from De la Cruz.

The next inning, Vanover angered Mets All-Star Jeff McNeil with a violation he did call. McNeil was waiting for baserunner Pete Alonso to retreat to first after a foul ball when Vanover dinged him for an automatic strike. That prompted an argument with McNeil and Mets manager Buck Showalter, who seemed irritated that the pitch clock began before Alonso returned to first.

It worked out for McNeil — he grounded an RBI single a few pitches later.

“I love the pace,” Scherzer said. “I don’t like the clock. I’ll double down on that. I think the umpire should have discretion to turn the clock off.”

MLB introduced the pitch clock this season to speed the pace of play. Players have 30 seconds to resume play between batters. Between pitches, pitchers have 15 seconds with nobody on and 20 seconds if there is a baserunner. Batters must be in the box and alert to the pitcher with at least eight seconds on the clock.

When a pitcher fails to throw a pitch in time, the penalty is an automatic ball. When a batter isn’t ready in time, it’s an automatic strike.

San Diego Padres star Manny Machado committed the first pitch-clock violation during spring training. Players were overwhelmingly encouraged by the new rules rollout during the preseason, when the average time of games fell 26 minutes to 2 hours, 35 minutes over the first three weeks.

Other changes this year include bigger bases to improve player safety, plus limits on infield shifts and pitcher disengagements to encourage more action.