Major League Baseball’s foreign-substance crackdown will arrive Tuesday night at Citizens Bank Park, as pitchers will be checked by umpires between innings to make sure they’re not hiding sticky stuff on their uniforms. The Mets’ Jacob deGrom had his hat, glove, and even his belt inspected on Monday night in New York, as the league launched the protocols. He passed the search, and the crowd booed the umpires. You can expect the same reaction in South Philly.

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— Matt Breen (extrainnings@inquirer.com)

Buyers or sellers? This week will help answer that

The Phillies are still more than a month away from the trade deadline, but the next week should play a big factor in determining the team’s approach on July 30.

They enter Tuesday four games behind the first-place Mets, who are the only team in the National League East with a winning record. A good week can push the Phils toward the front of the pack, and a bad week could bury them.

And it won’t be easy. They will line up Tuesday vs. Max Scherzer and the Nationals before facing the Mets four times this weekend at Citi Field. The Phillies lost four of their six games out west in a difficult road trip. This week is going to be another challenge.

The Nationals have won eight of their last 10 games, and the Mets should have deGrom on the mound this weekend. The second-place Phillies, third-place Nationals, and fourth-place Braves are separated by just one game. It’s a crowded race behind the Mets, and a bad stretch could make a team get lost in the shuffle.

“I think it’s a really important week,” manager Joe Girardi said.

The NL East was expected to be the best division in baseball, but it’s starting to seem likely that just one of the five teams will reach the postseason. That’s why the division games this week are so crucial. The Phillies have to keep up with the Nationals and Mets.

The trade deadline is still more than five weeks away, but it’s hard to imagine Dave Dombrowski being in a buyer’s mood if his team is under .500 and five, six, or even eight games back. That’s what a bad week can do.

The Phillies could use a starting pitcher, help in their bullpen, and a right-handed bat for the bench. But none of those moves would be worth it without a playoff spot in sight. Instead, the Phillies could look internally and see whom they can flip.

Archie Bradley and Vince Velasquez are both free agents after the season and could be valued by contenders. Brad Miller would give a playoff team a left-handed hitter who can play multiple positions, and perhaps Andrew McCutchen would want to finish off his contract in a playoff race.

For now, those players are still hoping that the playoff race will run through South Philadelphia. The next week will play a big part in determining if it will.

The rundown

As the Phillies brace for a pivotal week, Aaron Nola seeks a solution to his struggles, Scott Lauber writes.

Phillies super sub Ronald Torreyes credits his father for his unlikely big-league success, Lauber writes.

South Jersey’s mystery mud is the only foreign substance allowed by MLB to doctor baseballs.

Important dates

Today: Phillies open two-game series vs. Nationals, 7:05 p.m.

Tomorrow: Vince Velasquez starts series finale vs. Erick Fedde, 1:05 p.m.

Thursday: Phillies are off.

Friday: Phillies play doubleheader in Queens vs. the Mets, 4:10 p.m.

Stat of the day

Entering Monday, the Phillies had allowed the most two-strike home runs (35) in the National League and their opponents were hitting .176 with two strikes, the sixth-highest rate in the majors. Zach Eflin allowed a pair of two-strike homers Sunday.

“We talk about it all the time,” Girardi said. “We’ve given up way too many two-strike hits overall. Just mistakes. It’s something that if we’re going to get to the next level, we have to get better at that.”

“Bad execution. That’s really what it comes down to.”

From the mailbag

Send questions by email or on Twitter @matt_breen.

Question: Rhys Hoskins is so streaky every year and his defense isn’t good. Do you see him at first base for the Phillies after a year or two? — Dolores P. via email

Answer: Thanks, Dolores. Yes, I do. Maybe he’ll be sharing time at first base while also being the designated hitter, which the National League is expected to adopt in 2022. Yes, Hoskins is streaky, but when he’s hot, he carries the team.

The Phillies still have him under club control for two more seasons, which makes him an affordable option. Things could change — say the Phillies are 10 games back in July and a team inquires about Hoskins — but I don’t see him going anywhere.

Here’s a quote from last week by pitcher Zack Wheeler about the respect Hoskins has in the clubhouse: “Rhys has kept it professional the whole time. I know he’s been struggling but he always has a good attitude coming to the field, out there on the field. He doesn’t carry it out there into the field when he gets frustrated. You always kind of respect that.”