Kodai Senga and his troubles with walks and homers

Coming into the season, Kodai Senga was the big unknown in the rotation, as nobody was sure how his stuff would translate coming over to the U.S. With six starts under his belt, we’re still not really sure what to expect from Senga. His record is a nifty 4-1 but all six starts were against teams under .500 at the time they played. On top of that, the offense has mostly shown up when he’s taken the mound. The Mets average 4.27 runs per game but when Senga’s pitching, they’ve put up 38 runs, a 6.33 rpg mark.

In addition to his strong record, Senga sports a 3.38 ERA but again we have to figure in the quality of opposition. Eight of his 12 runs allowed have come in three innings, with the worst coming in San Francisco. The Mets staked Senga to a five-run lead and then he gave up four runs in the fifth inning. That frame highlighted the two main issues for Senga, as he gave up two homers and two walks.

In 32 IP this year, Senga has allowed 5 HR and 22 BB; both are alarming numbers. That’s a 1.41 HR/9 and again he hasn’t faced the top hitting clubs. What’s even more worrisome is that Senga has done a very good job of keeping the ball on the ground. He has a 53.7 GB%, the top mark among the club’s starters and the second-best mark on the entire staff.

Only 28% of his batted balls result in fly balls. The problem is that 21.7% of Senga’s flies leave the yard. MLB has a 12.3 HR/FB rate.

We can hope/expect that Senga will experience some regression with those HR/FB numbers. The walks are another beast. Throughout most of his career in Japan, Senga had elevated walk rates. His last two seasons showed improvement but his first year in this country have seen him have trouble consistently throwing strikes. He has a frightening 6.19 BB/9 and it’s not like it’s one or two outings blowing up the average. He’s yet to pitch more than six innings and he’s allowed either three or four walks in each start.

Senga’s best pitch is a splitter, one that’s frequently out of the strike zone. But he’s had issues throwing strikes with all four of his pitches, so it’s not fair to put all of the blame on the splitter. Besides, the splitter is supposed to end up a ball. The key to its success is to appear to be a strike before dropping out of the zone, generating swings and misses. He has a 10.9 SwStr%, overall, which is the same total as Justin Verlander’s lifetime mark in the category.

Going by FanGraphs’ Pitch Values, the splitter and cutter have been Senga’s best pitches, while his fastball and slider have both been negative pitches for him.

The righty pitcher has done a very good job with the platoon advantage, as he’s limited RHB to a .191 AVG and a .612 OPS. Lefties have been a different story, as they’ve posted a .769 OPS against Senga. Typically, pitchers throw their changeup when the batter has the platoon advantage. But while Senga threw a bunch of different pitches in Japan, the Mets have had him concentrate on just four here, with no changeup in his U.S. mix.

It will be interesting to see if after he gets more starts under his belt in this country if the Mets will reintroduce the changeup to his repertoire. Another thing that bears watching is who the team will pair as his batterymate. Tomas Nido has been Senga’s personal catcher, being behind the plate for all six of his starts. But Nido just went on the IL so it will be a different backstop later today.

The Mets called up Michael Perez to take Nido’s place and it seems likely that Perez will be behind the plate for Senga’s start this afternoon. Catchers typically get the day off with a day game following a night game. Plus, the Mets have bent over backwards to avoid pairing Senga with Francisco Alvarez, fearing that his tendency to throw balls in the dirt wouldn’t be the best thing for a rookie catcher.

But Alvarez has done a decent enough job behind the plate that it may be time to take off the training wheels and let him catch Senga. Hopefully he’s caught some bullpens with him, even if he has yet to catch him in an official game.

Senga has broken in under the most favorable conditions imaginable. The Mets have yet to pitch him on regular four days of rest, aiming to have him imitate his pitching regimen from Japan, where starters typically pitch just once a week. They’ve paired him with their top defensive catcher. If that’s not enough, the schedule has broken so he’s faced clubs that aren’t world beaters. And the offense puts on their hitting shoes when he takes the mound.

Now the Mets need Senga to take a step forward. They need him to consistently pitch six or more innings and give some rest to a beleaguered pen. And the key will be for him to reel in his free passes. Senga needs to stop walking so many batters if he hopes to see the seventh inning anytime soon. If he’s able to do that, he might keep his shiny ERA, even when he starts facing the good teams in the league.