ARLINGTON, Texas -- Jacob deGrom was stopped coming off the mound after retiring the side in order in the first inning, and chuckled as he handed his glove and cap over to the umpire. The New York Mets ace then undid his belt buckle as requested, showing there was no goop there either.

This was no sticky situation for the two-time National League Cy Young Award winner, only what will become a new norm for all professional pitchers.

The search is on for unauthorized foreign substances that pitchers can use to doctor baseballs, long against the rules but rarely enforced until now. The crackdown began Monday when major and minor league umpires started regular checks of all pitchers for tacky substances used to get a better grip on the balls, but can also increase the spin of the balls and make hitting them more difficult.

"I said, 'What all do you guys need?' 'Glove, hat and belt,' they said. I handed them that stuff and then went along my way," said deGrom, the first to get inspected since he was the first pitcher to take the mound on the day baseball's new enforcement directive went into effect. He started the first game of New York's home doubleheader against Atlanta.

The Mets and Braves were among 14 Major League Baseball teams who played Monday, six days after a five-page memo to teams about the pending change in enforcement that followed what baseball Commissioner Rob Manfred called an extensive process of repeated warnings without effect.

"I think I've seen everything in baseball, but this is new, setting a new precedent," said Houston Astros manager Dusty Baker, in his 24th season as a big league manager after 19 seasons as a player.

Asked whether such substances were tacitly allowed in the past, Baker responded, "You just didn't really make a fuss about it, but it was against the rules, so we'll see."

Rangers starter Kyle Gibson and Oakland's Frankie Montas weren't checked until after pitching in the second inning in Texas. Both were smiling after getting inspected on the field, and then getting a tap on the chest from plate umpire Dan Iassogna. They got checked again three innings later.

Texas manager Chris Woodward said before the game that Gibson said he has never used anything on a baseball.

"He's kind of a unicorn nowadays ... to have a guy who is so good who doesn't use anything," Woodward said. "It's probably rare."

Manfred said last week that the enforcement of foreign substances was needed "to level the playing field" after two months of comprehensive data collection, including inspections of balls used in games and testing by third-party inspectors. That came with the league batting average at a more than a half-century low along with record strikeouts.

Fans at Citi Field booed loudly when plate umpire Ben May halted deGrom on the pitcher's path off the field after the right-hander had two strikeouts in the first inning. After being cleared by crew chief Ron Kulpa, who had jogged in from third base to do the inspection, deGrom walked on to the dugout, laughing with catcher Tomás Nido about the exchange as the fans cheered.

Kyle Muller, who was making his first big league start for the Braves, was similarly stopped and inspected after the bottom of the first.

DeGrom appeared to ask May after the top of the second if he'd need to be inspected again, but May waved him on that time. He was inspected again after the fifth, prompting more boos from the fans while their hometown pitcher was cleared again.

"Honestly, I didn't mind it. It was quick and it went pretty easy," deGrom said.

There was a strange occurrence in Phoenix when Milwaukee left-hander Brett Anderson was checked by umpires while leaving in the middle of the second with an undisclosed injury.

Anderson was slowly walking off the field when he was approached by plate umpire D.J. Reyburn. After his glove and cap were quickly checked, the pitcher was allowed to go to the dugout.

The umps had inspected Arizona starter Merrill Kelly after the top of the second.

Any suspended players would not be replaced on a team's active roster. Braves manager Brian Snitker emphasized that when he met with players Sunday and discussed crackdown at length.

"I think the biggest thing we wanted to reiterate is if you get popped, we can't replace you," he said Monday from New York. "That's a big deal. I think everybody's aware of what's going to go on and how serious it is, to not mess around and get suspended, because that's a definite blow to your club when you got to go short like that."

Chicago Cubs manager David Ross, a former big league catcher, was asked whether hitters needed to be more careful in the batter's box due to potentially slicker baseballs.

"So the information so far in the last 10 days, batting average has gone up, on-base has gone up, (slugging percentage) has gone up. Spin rates are down on fastballs, breaking balls, and hit by pitches are exactly the same," Ross said. "So you draw your own conclusions."

Cleveland Indians manager Terry Francona, who was not worried about any issues with his pitchers, figured that everybody around the league would be on their best behavior with everyone watching the first night.

"I'm sure there's going to come a day when it's a hot day and everybody's a little irritable that something will probably happen," Francona said. "MLB's been pretty open that there might be a hiccup or two. But I do think for the most part, I think the majority of everybody wants the same thing. Just how you get to it some days, you know, you're dealing with competitive people and sometimes you get your ire up a little bit or something. Something will happen, I'm sure."