We’re officially in the heart of callup season.

Thanks to rosters expanding and some teams already beginning to plan for next year, there have already been 23 debuts so far this month, with more undoubtedly on the horizon. With that in mind, here are 13 of the most thrilling, productive and even historic player debuts so far this season.

Note: All stats are through Sunday’s games.

Spencer Steer, Reds
2-for-2, HR, 2 BB, scored game-winning run (Sept. 2 vs. COL)

In a month full of rookie debuts, Steer’s might be the most memorable. The main return in the Tyler Mahle trade, Steer didn’t take long to endear himself to Cincinnati fans, becoming the first Red to reach base four times in a Major League debut since Jay Bruce in 2008. He also became the first Cincinnati player to reach base four times with a homer in his debut along with being the first Red to score a walk-off run in a debut since Otto Bluege in 1932.

Hunter Brown, Astros
6 IP, 3 H, 0 R, 1 BB, 5 K (Sept. 5 vs. TEX)

On Aug. 30, the Astros placed AL Cy Young Award candidate Justin Verlander on the 15-day IL with a right calf injury. Five days later Brown did his best Verlander impersonation in his debut, tossing six electric innings in Verlander’s spot in the rotation. Brown baffled the Rangers in his first start, relying mostly on his fastball (which averaged 96.1 mph) and slider (which averaged 93 mph and topped out at 95.7 mph). He became the third Astros pitcher to throw at least six scoreless innings in his debut, joining Carlos Hernández (2001) and Jarred Cosart (2013).

Ryne Nelson, D-backs
7 IP, 4 H, 0 R, 0 BB, 7 K (Sept. 5 at SD)

Three hours before Brown stymied the Rangers, Nelson put together a memorable debut of his own by tossing seven scoreless innings against the Padres. In the win, Nelson became the second pitcher in AL/NL history to throw at least seven innings and record seven strikeouts while allowing zero runs and walks, joining Pittsburgh’s Nick Kingham. In fact, Nelson’s only three-ball count came in the seventh inning against Josh Bell. Not bad for your first time on a Major League mound.

Vaughn Grissom, Braves
2-for-4, HR, 2 RBIs, SB (Aug. 10 at BOS)

While fellow Atlanta rookies Spencer Strider and Michael Harris II have (understandably) garnered a lot of attention this year, Grissom has also been crucial to the Braves’ success. At just 21 years old, Grissom became the youngest player in AL/NL history to homer and swipe a bag in his debut along with becoming the first Braves player in the modern era to homer and steal a base in his first game. Grissom also flashed his potential with the leather by turning two double plays at second base despite only playing seven games at the position in the Minors.

Gunnar Henderson, Orioles
2-for-4, HR (Aug. 31 at CLE)

While Henderson wasn’t the first big-name prospect the Orioles called up this season, he's one of the few who made his debut in the middle of a stretch run. Henderson, who was Baltimore’s top prospect and the No. 2 prospect in baseball at the time of his callup, wasted no time making an impact: His first hit came in the form of a mighty home run against Triston McKenzie. With his home run, Henderson became the first Oriole since Trey Mancini in 2016 to homer for his first big league hit, joining Jonathan Schoop and Larry Haney. He also lost his helmet in the process, which allowed for him to show off his big league flow.

Brett Baty, Mets
2-run HR in 1st MLB at-bat (Aug. 17 at ATL)

With the Mets locked in a tight division race against the Braves, Baty made an immediate impact by going deep on the first pitch he saw in the Majors, joining Mike Jacobs, Kazuo Matsui, Mike Fitzgerald and Benny Ayala as the only Mets to homer in their first career at-bats. While Baty went hitless for the rest of his debut, he still showed his power with a 113 mph line drive off left-hander Tyler Matzek -- the hardest-hit ball by a Met in a left-on-left matchup since 2016.

Wynton Bernard, Rockies
1-for-3, SB (Aug. 12 vs. ARI)

After 863 Minor League games, Bernard finally got his chance in the bigs and immediately made history. At 31 years and 322 days old, Bernard became the oldest player to get a hit and steal a base in his Major League debut since the Cardinals' Joe Delahanty on Sept. 30, 1907 (31 years, 347 days). After bouncing around in the Minors with four organizations, Bernard signed with the Rockies last year, hitting .254 with Triple-A Albuquerque. This year, Bernard tore up Triple-A, batting .325 with a .962 OPS in 87 Triple-A games before getting the call to The Show.

James Outman, Dodgers
3-for-4, 2B, HR, 3 RBIs (July 31 at COL)

For one day, Outman was the best slugger in the Dodgers’ stacked lineup. In his first MLB plate appearance, Outman crushed a ball 405 feet to right-center field to become the eighth player in franchise history to hit a home run in his first at-bat, and the first since Keibert Ruiz on Aug. 16, 2020. Outman added two more hits in the later innings, a seventh-inning single and an eighth-inning RBI double. He became the first Dodger to have three hits, a home run, three RBIs and two runs scored in his MLB debut. Not bad for a guy who said he once swung like a caveman.

Jerar Encarnacion, Marlins
Recorded grand slam, outfield assist and SB (June 19 at NYM)

Prior to Encarnacion’s debut, Marlins manager Don Mattingly compared him to Hall of Famer Vladimir Guerrero. Encarnacion didn’t waste any time making good on that comparison, mashing a go-ahead grand slam for his first Major League hit in Miami’s 6-2 win. Earlier in the game, Encarnacion flashed the leather with a 91.7 mph assist to nab Tomás Nido at second base, the third-hardest outfield assist for the Marlins in 2022. He also recorded a stolen base, making him the first AL/NL player to hit a grand slam, steal a base and record an outfield assist in his MLB debut.

Adley Rutschman, Orioles
1-for-3, BB, 3B (May 21 vs. TB)

The No. 1 prospect in baseball at the time of his callup, Rutschman’s first career hit came on a triple down the right-field line that showed off the sweet swing that helped him fly up prospect rankings. He became the first catcher to triple for his first hit since Brad Davis of the Marlins in July 2010 and joined Manny Machado and Matt Wieters as highly touted Orioles prospects who also introduced themselves with a triple.

Christopher Morel, Cubs
Pinch-hit HR (May 17 vs. PIT)

Morel’s first at-bat was like something out of a movie. With the Cubs dealing with a rash of injuries in the middle of May, Chicago’s brass decided to call up Morel, with his first at-bat coming as a pinch-hitter in the eighth inning of a game against the Pirates. After working an 0-2 count to a full against Chase De Jong, Morel crushed a fastball to the left-field bleachers, setting off a wild celebration at Wrigley Field. Morel became the first Cub to homer in his first career at-bat since Willson Contreras on June 19, 2016, a stat that’s even more sweet considering Contreras was one of the first players out of the dugout to celebrate with Morel.

Chase Silseth, Angels
6 IP, 1 H, 0 R, 2 BB, 4 K (May 13 at OAK)

The first player from the 2021 Draft to reach the Majors (and therefore the first of the 20 pitchers the Angels selected that year to debut), Silseth dazzled against the A’s, striking out four and walking two before being removed after 81 pitches. With the strong start, Silseth became the second player in Angels history to throw at least six innings while allowing no more than one hit in a Major League debut, joining Rudy May, who threw nine one-hit innings in his first game against the Tigers on April 18, 1965.

George Kirby, Mariners
6 IP, 4 H, 0 R, 0 BB, 7 K (May 8 vs. TB)

It’s hard to believe now, but there was once a point in the season where the Mariners were struggling. With Seattle looking for an early-season jolt, the team's front office turned to Kirby, then its No. 3 prospect. Kirby looked the part from the beginning, striking out three in the first before throwing five more scoreless innings in Seattle’s come-from-behind win.