Yesterday I made a point on Twitter, repository of good points, that we shouldn't assume Strasburg "never came back" from Tommy John surgery* because he didn't pitch enough in the majors to give us a baseline. Of course it may be just as reasonable to argue the flipside then. We can't argue he did come back because we don't know where he started from. Where do the arguments come from? What ultimately makes most sense?
Let's start with the base argument for the "never came back"ers. Before Tommy John surgery Strasburg was averaging 97.6 MPH on his fastball. After returning from the surgery he was averaging 96 MPH. The 1.5 MPH drop has to be explained by something.
But that 97.6 MPH average was only done in 68 innings. Could it be an amped up rookie performing for the crowd? To answer that we need his minor league data.... that doesn't exist**. Even if we had his numbers it would be tough to say anything definitive with just that. It could be the case that he's more dominant in the minors which leads to fewer pitches thrown which leads to the ability to throw the pitches he does throw harder. Really what we need is ALL minor league data so we can see, based on age and minor league numbers, what we would expect a pitcher to do in the majors. Then we need to compare Strasburg's trajectory to the expected one and see if we can reasonably say TJ surgery threw him off. But all I'm doing now is going further down a rabbit hole with no rabbits. Doesn't exist.
Oh well. What kind of comparison can we do? Well we could find any other young MLB stud starter that has averaged that level of fastball and see if they tailed off as much in the first two years. That would at least give us something.
That ends up telling us something that might be pertinent. You see before last year, when Yordano Ventrua averaged 97 MPH even on his fastball - no one averaged faster than 96.1 MPH (as long as we have this data for which is like from 2001). And yet we're going in assuming Strasburg would average 97.6 for a season? That seems unreasonable. That 2010 Strasburg would be THAT much faster than anyone had ever thrown for a season? This seems to indicate that that 97.6 MPH number was simply unsustainable over the course of a major league season.
Of course if Strasburg WAS special and could average a fastball that much faster than everyone else than that drop in velocity would be something. In general pitchers roughly stay close to peak velocity through their late 20s and don't see many drops as large as a 1.5 MPH in their early 20s. That would be unusual, if that's what you believe.
What about monthly speeds in 2010? If those dropped then it would lead us to a similar conclusion. In fact, though, they DON'T drop. Strasburg averaged 98 MPH in June, 97.7 in July, and 98.1 in August. That's pretty consistent. Then again his IP per game was dropping quickly. In June it was 6 1/3. In July it 5 2/3rds. In August it was around 4.5 IP. Remember the minor league argument; fewer pitches means you can throw harder.
What about his other pitches? Again there is too little major league data to be sure but it appears that the velocity drop was across the board but the movement on his pitches remained about the same. Or at least we can't claim from the data any significant changes. The exception may be his change-up, which went from a a very tight pitch with little vertical movement to one with noticeable vertical movement. Of course who's to say what's better and the pitch has remained effective.
We're basically left nowhere at this point. Either argument is arguable. He was throwing superhumanly fast before Tommy John. He threw only as fast as the fastest after. Was it the surgery? I tend to lean toward no because I look at the history of baseball and think Strasburg can't be that much of an outlier compared to all the other pitchers who threw over the past decade plus. That's the base assumption, and I think if your data is inconclusive that's the best assumption to make. But if you want to argue the other side I can't really tell you you're wrong.(but I can still say you shouldn't seem so sure about it)
There are other things to think about to. Perhaps he could hit the same speed after surgery but was explicitly coached to take it down a notch. Perhaps he could have thrown that fast for a season but perhaps it was that speed that led to the injury. Maybe he had the talent but the physical tools just didn't exist for him (don't exist for anyone?) so the argument would be he would have always become the pitcher he is today.
One thing to remember. I talk a lot about impressions and how fans feel about a player being shaped by key moments; his first few appearances, his work in big games. For all the sepia-toned nostalgia that goes with Strasburg's first season arguably his best two starts were his first and his third. After those two, super fast fastball or not, he would never go over 6 innings with a ton of K's and low runs given up again. (he had a handful of great starts that only lasted 6IP). The Strasburg you may remember, the dominant force that would shut down teams deep into games, never existed.
*for those that don't run in the same Twitter circles this has been a theory slowly growing in popularity.
** Fall League numbers in 2009 do exist and he was up OVER 98 MPH but this was literally 120 pitches total. I have a hard time considering that comparable, so I don't think it should be used either as evidence that 97.6 MPH was reasonable for a season or evidence that his overall MPH was dropping. We could check vs other Fall League pitchers if you like.