Here are the 10 hottest rookies over the past 30 days

September 6th, 2023

Welcome to the September edition of the MLB Pipeline Rookie Hot List. As we’ve done four previous times this season, we will highlight the top-performing rookies of each month.

As the calendar changes, we wipe the slate clean for every rookie, giving each newcomer an equal shot -- and the seven players on this list who did not appear in the August edition certainly made the most of it. In fact, Toronto's didn't make his big league debut until Aug. 4.

But before diving into the list, a quick reminder: this exercise does not look at who is most likely to come home with the Rookie of the Year Awards. That can serve as a tiebreaker, but we’re primarily looking at which rookies performed best over the past 30 days (using stats through Monday’s games).

Some names that just fell shy of the cut, but deserve some recognition as honorable mentions are (in alphabetical order): Nolan Jones, Bobby Miller, Grayson Rodriguez and Anthony Volpe.

But here are the 10 top-performing rookies over the past 30 days:

1. , 1B, Red Sox (previous rank: 1): Holding on to the top spot for the second month in a row is Casas, whose performance not only elevated him into the Rookie of the Year conversation, but also is a big reason why Boston is six games over .500 and still in the hunt for the final Wild Card spot. The 23-year-old posted a 1.019 OPS over his past 27 games and he's been slotted into the Red Sox cleanup spot in the order.

2. , RHP, Mets (previous rank: 4): With all of the ups and downs that the Mets have experienced this season, one thing they could always count on was Senga giving them a chance to win every time he took the hill. The standout righty from Japan not only was named an All-Star in July, but he continues to improve; over his past five starts, he's yielded two earned runs or fewer four times. He's also improved on his control issues that plagued him earlier in the year, allowing just 11 walks and two home runs over his last five outings (32 2/3 frames).

3. , OF, Cardinals (previously unranked): There is very little that Walker didn't do to impact games for St. Louis over the past month. Putting all five of his tools on full display, the 21-year-old slashed .313/.391/.550 with 10 extra-base hits and 13 RBIs. He also created havoc on the basepaths, consistently made highlight-worthy defensive plays and used his arm to keep opposing runners honest. Since getting recalled to the big league club on June 2, this is the best Walker has looked.

4. , OF, D-backs (previously unranked): Carroll is no stranger to this list, and after missing it in August, he is right back near the top. A clear frontrunner for the National League Rookie of the Year, the 23-year-old fortified his case last week when he became the fourth rookie in AL/NL history with at least 20 home runs and 40 stolen bases in a season. He also became the first D-back to have a 20/40 season since Eric Byrnes in 2007.

5. , 3B, Twins (previously unranked): You might have expected to see Lewis a little higher on this list because no one in baseball had a more eventful (or exciting) eight-game stretch when he connected on three grand slams and posted four games with at least four RBIs -- including a six-RBI effort on Monday. However, he did only appear in 18 games, which was considered when slotting him fifth.

6. , RHP, CHC (previously unranked): Assad just missed making this list last month, but his performance was still worthy of an honorable mention. Now, the right-hander left no doubts about his place among the top rookies. The 26-year-old is one of the main catalysts for the North Siders' surge in the standings -- they currently sit in the second Wild Card spot in the NL. Assad made six starts over the past month and allowed two earned runs or fewer each time out. His most recent start was the best of his career as he posted eight scoreless frames with seven punchouts against a very potent Reds lineup.

7. , C, Astros: (previously unranked): Diaz is another rookie whose effort has been a driving force in his club's recent surge. The Astros not only sit in the second Wild Card spot in the AL, but they have also pulled into a virtual tie for the lead in the AL West. Diaz is slashing .310/.344/.598 with seven home runs and 20 RBIs over his past 24 games. His .942 OPS ranks fourth among all rookies who have played at least 15 games over the past month.

8. , SS, Orioles (previously unranked): When Henderson's name didn't appear on last month's list, it felt like an aberration. Another player consistently mentioned in the AL Rookie of the Year conversation, the 22-year-old continues to do what he does -- impact baseball games from wherever he is standing. Henderson clubbed five more home runs to bring his tater tally on the year to 23, while also claiming the Play of the Week (below) after turning a double play that resulted in the speedy Corbin Carroll being thrown at the plate.

9. , INF/OF, Blue Jays (previously unranked): The aforementioned Schneider is only 18 games into his Major League career, but boy has he made them count. The 24-year-old went yard in his big league debut, homered again two games later and already has a three-game homer streak that turned into four in five games in late August. His 1.330 OPS leads all rookies with at least 15 games played over the past month, and we haven't even mentioned the legendary 'stache that is becoming its own phenomenon north of the border.

10. , 2B, Athletics (previous rank: 8): Gelof has really tapped into that 60-grade power tool that he flashed throughout his time in the Minors, and may have even added a tick to his 55-grade hit tool since debuting in The Show. The 23-year-old belted five more dingers and led all rookies with 57 total bases over the past month. His performance also earned him AL Rookie of the Month honors for August.