There has been a lot of discussion on Twitter recently about streaming pitchers particularly after everyone got Gombered. Too often we fall in love with treating our last rotation spot like a pump and dump campaign hoping to maximize its value. However, this will often lead us to drop a pitcher who may be in the midst of a genuinely real breakout. Finding those guys is the true goal of these location reports. This week we are going to talk about a favorite pitcher of mine in David Peterson.

I typically decide who I want to write about on Mondays and that meant I picked Peterson before his best start of the season Tuesday against the Red Sox. However, while the start lowered his ERA to a more manageable 5.59, the skills that had me interested after his first three games were no longer present. Peterson was great in 2020, pitching to a 3.44 ERA as a rookie and showing what appeared to be real contact suppression skill. If you have followed baseball at all over the last few seasons, you know that contact quality suppression is not exactly “real”. Unsurprisingly, Peterson has swung back in the other direction in 2021, and his elevated ERA is due to a sudden HR issue. Before the Boston start, however, what made me interested in Peterson was new found ability to generate Ks. When evaluating his full-season potential, this is the question we need to answer.

David Peterson

When looking over his Savant page, it’s easy to see that Peterson has not made any of the pitch mix changes we typically align with a jump in strikeouts. In fact, he has actually done just the opposite. He has ditched his four-seam fastball almost exclusively for a sinker. Looking over the data it is pretty easy to see why, Despite the pitch having success in 2020, hitters thus far has crushed the fastball to the tune of a 0.698 wOBA and an xwOBA of 0.665. The problem for the fastball largely seems to be location.

As you can see above, this is the chart for Peterson’s fastball locations. This chart includes not only the four-seam fastballs but the sinkers as well. Looking over this chart you can see that is abundantly clear why his fastball is getting torched. In almost every one of the count charts, there is a small cluster of fastballs being left almost directly over the heart of the plate. Peterson has an xLwOBA of 0.357 on the four-seam which is in the bottom third for all pitchers in baseball thus far. The pitch is not special enough to survive being located poorly. He locates the sinker decently well and has managed to attack the edges of the zone with it so he should continue sticking to the pitch.

However, as a whole, Peterson’s xLwOBA (location-based expected wOBA) is unchanged from 2020. Both years he was right around league average and that leads us to an interesting conclusion, Peterson will likely always be at the mercy of “luck”. His success will largely be defined by if he can keep the ball in the yard. However, all that changes if he can improve his K rates, and thus far he has done just that. The switch to the sinker has actually been a positive one for him as his sinker is actually one of the best in baseball. By swinging strike rate, Peterson ranks 17th among those who have thrown over 100 sinkers. This is only two spots behind Dustin May. Typically, with a pitcher like Peterson, I want to see a change in his xWhiff. This likely means that any improvement in K% is driven by a subsequent improvement in the ability to locate. With Peterson, we are not seeing that, once again he is largely unchanged. The stuff as a whole does not even appear to be playing up.

So where are the newfound strikeouts coming from? The strikeouts at least appear to be partially driven by a new overall approach from Peterson. He is attacking the zone more often which is leading to a higher overall swing rate but is also leading to more called strikes. This is evidenced by his CSW% of 30% higher than last season’s 27%. The more strike happy approach seems to be doing wonders for his K and BB rates but it may also be a huge part of the season why Peterson is allowing more homers. He may be a pitcher who will benefit greatly from a few more walks allowing him to avoid the heart of the plate often.

Overall, I went into this article hoping to leave much more excited about David Peterson than I really am. His K% and BB% have greatly improved thus far but they do not seem to be backed up by the type of skill improvements that are sustainable. He will likely be a much more effective pitcher if he avoids the zone more often, trying to avoid allowing the long ball. StuffERA still likes him way more than FIP or other traditional ERA estimators but this version of Peterson is more of a low 4 ERA type than the mid to high 3 ERA guy we saw last season. If the stuff comes back to playing up a bit (In_Whiff above 0) then Peterson is a guy to keep an eye on in season-long leagues. I am still holding but I am certainly nowhere near as excited as I was even just a week ago.