MLB trends: Mets’ home run trouble, Giants’ velocity problem and the changing face of starting pitchers

Memorial Day has come and gone and we’re now into the meat of the 2025 MLB regular season. The sample sizes aren’t especially small anymore, contenders and pretenders have begun to establish themselves, and we’re almost exactly halfway between Opening Day and the trade deadline. Here now are three trends worth keeping an eye on as we get closer to the calendar flipping to June.

Mets‘ starters running into home run trouble in May

May has been a bit sluggish for the Mets, who were 12-11 with a plus-6 run differential this month heading into Tuesday’s game with the White Sox. That’s not bad by any means. When your sluggish 23-game stretch is a .500 record and not, say, 6-17, you’re pretty good. The Mets play seven of their next 11 games against the White Sox and Rockies. Wins are coming.

One thing that is catching up to the Mets this month (and not unexpectedly) is the home run ball, particularly with their starters. New York’s starting pitchers allowed six — six! — home runs in 31 games in March and April. Every other team’s rotation allowed at least 14 home runs in the season’s first month. In this homer-happy era, Mets starters did incredible work keeping ball in the park.

Reliable batted ball data goes back to 2002. Here are the lowest March/April home run rates since then (starting pitchers only):

It is no coincidence that the rotations that best prevented home runs in March/April were National League teams before the universal DH was fully implemented in 2022. Among teams in DH leagues, New York’s starters just had the best homer prevention March/April since the 2013 Tigers, who had peak Anibal Sánchez, Max Scherzer, and Justin Verlander in the rotation.

Predictably, New York’s starters have begun to regress to the mean in the home run prevention department. In May, their starters rank 17th with 1.12 HR/9 and 20th with 12.9% HR/FB. They’ve given up 15 homers in May after allowing just six in March/April. To put it another way, their starters gave up six homers in their first 33 games and 15 in 21 games since, entering Tuesday.

Griffin Canning, Clay Holmes, and David Peterson are above-average ground ball pitchers you would expect to run lower-than-usual home run rates. As low as they were in March/April though? No, probably not. That was “good ground ball pitchers who also had some good fortune keeping the ball in the park” thing. Now that the season has a chance to breathe, they’re leveling out.

The league home run rate rises as the weather warms up and Mets’ starters were never ever going to maintain a 0.35 HR/9 and 4.7% HR/FB for 162 games. Given the personnel, the expectation moving forward should be a rotation that prevents homers at an above-average rate, but not at one of the best rates ever. March/April happened and you can’t take that away, but it was a bit anomalous.

SF has a velocity problem

Despite taking a 31-23 record into Tuesday night’s game with the Tigers, it has been tough sledding for the Giants offensively the last few weeks. They had not scored more than four runs in a game since May 17 and were hitting .237/.310/.376 as a team in May. That works out to a 93 OPS+ once adjusted for pitcher-friendly Oracle Park and other factors.

The Giants will need to score more runs moving forward to have their best chance at returning to the postseason for the first time since 2021. And to score more runs, they have to do a better job against fastballs, particularly high-velocity fastballs. No contender in baseball has had less success on 95 mph fastballs this season than San Francisco.

Here are the numbers entering play Tuesday. This is on four-seam fastballs and sinkers at 95 mph and above:

Expected weighted on-base average, or xwOBA, is a good quick-and-dirty measure of contact quality based on exit velocity, launch angle, etc. It is scaled to on-base percentage, so a .400 xwOBA is elite, .350 is really good, .300 not so much, etc.

Only the very bad White Sox (.195) have a lower batting average against 95 mph heaters than the Giants. The White Sox (.308) and Braves (.322) are the only teams with a worse slugging percentage. Just ahead of the Giants are teams like the Athletics and the surprisingly offensively inept Rangers. Not the company you want to keep, basically.

By xwOBA, San Francisco’s best hitters against high velocity fastballs are the guys who should be their best hitters: Willy Adames (.364) and Heliot Ramos (.376). Ramos was an All-Star last year and Adames was the offseason’s big free-agent signing. The laggers are basically everyone else, including Matt Chapman (.310), Jung Hoo Lee (.304), and Mike Yastrzemski (.280).

The Giants have gotten very little production from first base this year: .186/.292/.322 with four home runs. That is an obvious spot to upgrade at the deadline and someone like Rhys Hoskins (.402 xwOBA vs. 95+ mph) or Ryan O’Hearn (.352) would make sense given their ability to handle the heat. It’s a clear need for a Giants team that has been very good at keeping runs off the board, and no so great at scoring them.

Welcome to the five days’ rest era

There has been one constant throughout baseball history: Pitchers throw less and less with each passing year. Just about everything else in this game is cyclical, but pitcher workloads? No, they only go in one direction, and that’s down. Only four pitchers threw 200 innings in 2024. Go back 10 years to 2014, and 34 guys got to 200 innings. Workhorses are few and far between.

Last year’s Dodgers came pretty close to running a full-time six-man rotation. They regularly used spot starters and bullpen games to give their starters additional rest throughout the summer. The Cardinals used a six-man rotation this April. The Tigers have used one at times this season too. Other clubs have used a sixth starter now and then to build extra rest into the schedule.

As a result, pitchers across the league make fewer starts on four days’ rest. Five days’ rest is almost becoming standard. Here are the percentage of starts on normal rest and five or more days of rest the last few years:

Those percentages do not add up to 100%. Blame openers. They frequently start on fewer than four days’ rest and those starts don’t fit into either of our two buckets in the table.

Anyway, 2021 was a bit unusual because of the pandemic. Teams were understandably worried about their pitchers following the 60-game season in 2020 and handled them carefully. After a “normal” season in 2021, teams were comfortable asking their pitchers to make more starts on the usual four days’ rest in 2022, and things have gradually trended down from there.

A decade ago, in 2015, 46.7% of starts were made on normal rest and 52.0% were made with at least five days’ rest. Not quite a 50/50 split, but close, and nowhere near this year’s 30/70-ish split. Fewer than three out of every 10 starts this season are made on normal rest. To put it another way, pitchers are more than twice as likely to start on extra rest than normal rest now.

Six-man rotations have not yet fully taken hold. These extra rest starts are also made possible by off-days. The current collective bargaining agreement added four more off-days to the schedule and teams rarely use off-days to skip their No. 5 starter. In the past, it was common to see teams use a four-man rotation for weeks at a time thanks to off-days. No more though.

Also, the minor-league schedule changed in 2021. Now every Monday is an off-day in the minors. Minor-league pitchers get that guaranteed extra rest each week and make very few starts on normal rest. Pitchers are simply no longer being trained to start on normal rest, and the downstream effect is fewer normal rest starts in the big leagues. This is really only the beginning.

All the extra rest starts have not significantly reduced pitcher injuries and part of it is the extra rest allows starters to empty the tank more frequently, and make more max effort pitches. It’s a bit of a self-fulfilling prophecy. Extra rest to keep guys fresh and at their best, which then allows them to throw harder when they do pitch. Injury reduction has been minimal at best.

It is only a matter of time until six-man rotations become the norm. I don’t know if that’ll happen in five years or 15 years or 50 years, but it will happen one day, the same way four-man rotations became five-man rotations in the 1970s. We are in the very early stages of the six-man rotation era now. Pitchers are making fewer starts on normal rest than ever.