It’s not an outlandish question to ask. Over the last 30 days, which spans five starts and 32.1 innings, Marcus Stroman has posted the third highest strikeout rate in baseball and the lowest SIERA. Five starts is a tiny sample size, of course, but you can’t fake a high strikeout rate. Let’s go back a little further. Since my cherry-picked date of June 14, he has made 12 starts and has posted a strong 25.2% strikeout rate, low 4.2% walk rate, elite 61.5% GB%, and impressive 2.82 SIERA. You know who else has combined that type of strikeout ability, pinpoint control, and serious ability to induce grounders? Nobody.

Felix Hernandez is probably the best comp as he has typically posted ground ball rates in the 50% range, while striking out 20%+ of the hitters he faced. But he has only once posted a ground ball rate above 60% in a season and his walk rate never fell below 5.0%. Ground ball pitchers typically throw sinkers often and are the so-called “pitch to contact” types, hoping their defense converts their balls in play into outs around 30% of the time.

Up until this recent streak, Stroman had been that type too. He was toward the upper echelon of strikeout artists given his ground ball rate, but was still no better than league average. Despite flashing an assortment of pitches, they simply didn’t generate the swings and misses you would expect. But with the ground ball foundation and good control already there, the potential was apparent for future stardom.

Of course, looking at his season as a whole, you wouldn’t think stardom is on its way. Or even close. He owns a poor 4.47 ERA and he hasn’t been able to keep his fly balls in the park. But things have changed during the season. A couple of weeks ago, Eno Sarris looked into the changes he made to his pitch mix, along with the improvement in velocity, movement, and spin.

Like I did with Danny Duffy last week, let’s take a look at Stroman’s season before and after my June 14 cut-off date.

Marcus Stroman 2016 Performance Date Range GS FB% FBv SL% SLv CT% CTv CB% CBv CH% CHv LD% GB% FB% IFFB% 4/3 – 6/9 13 59.2% 92.0 10.4% 84.7 12.1% 89.6 9.6% 80.3 8.7% 83.9 20.2% 59.2% 20.6% 3.5% 6/14 – 8/21 12 55.6% 92.7 21.0% 87.4 10.2% 89.7 9.4% 81.9 3.7% 86.3 17.8% 61.5% 20.7% 0.0%

I decided to highlight anything that went down in red and anything that went up in yellow. Down isn’t automatically bad (like for pitch selection), but it was easier to identify the trend with so many metrics.

As Eno noted in his article, Stroman has gained velocity, and it shows in every one of his pitches except his cutter. More velocity is nearly always a good thing. Of course, velocity tends to across as the season progresses, so this isn’t really too surprising. Still, it’s a good sign, and certainly better than stagnant velocity or even a loss.

The next big change was that he has doubled the usage of his slider, at the expense of all his pitches. In his only other full season in 2014, his slider generated the highest SwStk% of any of his pitches. It also induced grounders 61% of the time! Whiffs and ground balls? That’s an elite pitch, folks. So it’s about time Stroman, or perhaps the Blue Jays organization, realized this and he now uses it as his primary non-fastball. Although his SwStk% on the pitch is down marginally from 2014, it’s still above average and the best of his secondary pitches. And yet again, it’s a worm-killer, generating a 57.4% ground ball rate.

The only real knock on him is his inability to generate pop-ups. That wasn’t a typo — he is still looking for his first pop-up since June 14. Ground ball pitchers generally have low IFFB% marks, but Stroman’s is frighteningly low and offsetting some of the benefit of his strikeouts.

Now let’s check on the results of these pitch changes:

Marcus Stroman 2016 Performance Date Range GS Hard% F-Strike% SwStk% K% BB% BABIP LOB% HR/FB ERA SIERA 4/3 – 6/9 13 32.4% 58.8% 8.2% 15.7% 7.1% 0.306 64.1% 12.3% 4.13 4.13 6/14 – 8/21 12 32.3% 62.5% 9.9% 25.2% 4.2% 0.320 74.1% 25.0% 3.94 2.82

So far, throwing the slider more often hasn’t suppressed hard contact at all. If you hop over to the HR/FB rate column, you see that despite a nearly identical Hard%, his HR/FB rate has doubled to a ridiculous level. What the slider seemingly has done (and the velocity bump, I’m sure), is boost his SwStk%, and ultimately, his strikeout rate. He is also throwing more first pitch strikes, which has pushed his walk rate down.

You can see in the ERA column that it has been easy to overlook what Stroman has done if you weren’t paying attention. That inflated HR/FB rate, paired with a BABIP well above .300 has ensured that his ERA improve by only a minor amount from his pre-June 14 games, leading to a significant ERA/SIERA gap. The high BABIP isn’t entirely bad luck, as I discussed above his embarassing lack of pop-ups that make for near automatic outs. A high ground ball rate also isn’t great for BABIP and ground balls have a much higher BABIP than fly balls do. I’m sure the pop-up issue improves and he’s probably not a true talent .320 BABIP guy. And he’s definitely not a 25% HR/FB rate guy!

So what we have in Stroman is what made us all excited in the first place when he debuted a couple of years ago. He possesses a vast repertoire that he’s still playing around with to find his most effective mix. He induces gobs of ground balls, so even with a high 17.8% HR/FB rate on the season, his HR/9 is still well below the league average. His control has always been good and now all these additional sliders have made him an above average strikeout pitcher too.

He may just be the perfect pitcher. The best in baseball? It’s certainly possible, at least while Clayton Kershaw remains sidelined.