Rookie Renaissance

Right now, wherever you look in the MLB media landscape you will see someone talking about the current crop of rookies. Most, if not all of these articles will be talking about how amazing these guys are and some are suggesting it is the best set of rookies we have seen in a while.

Sports fans and media are often drawn to hyperbole when talking about young/new players, so let’s look at the data to see if this hyperbole is more reasonable than it seems. I will be looking a data from the 1998 expansion onwards to determine if this is really the case.

The graph above shows the percent of WAR in each season that rookies were responsible for. You can see that levels for hitters inline with previous years and the pitchers are down. But we should account for the fact that rookies get a different amount of playing time in the second half of the season compared to the first, thanks to service time manipulation.

The rookie WAR percent for hitters in the second half of 2018 was 15.1% compared to 3.2% for the first half. Based off that I would have expect 2019 to be lower than average for this season so far, but the percentage for 2019 hitters is already in the normal range for most years (except 2015). So, we are seeing an increased production from rookie hitters.

The same cannot be said for pitchers. Although they do see an increased workload in the second half in 2018, we didn’t see an increased WAR percentage, so this dip for 2019 pitchers could be real. The volume of innings pitched is inline with previous seasons, so it isn’t a factor of the rookies get less time. This suggests that the crop of pitching rookies this isn’t as good as normal. Continuing a trend seen over the last few seasons.

That is looking at things from an overall perspective, a lot of the chatter about the rookies is focused on a few individuals. So are the top rookies this year better than the top rookies we have seen previously.

Let’s look at hitter first. I took every rookie that had more than 100 PA for every season since 1998 and bucketed them based on their fWAR.

From this we can pull a few titbits. This data was taken from after the games on the 11th August and there are already more rookies with 100 PAs in 2019 than a couple season in the last 20 years.

The 2015 season was strong in WAR not just because of one player getting a really high total, but there being a lot more than normal getting 1+ WAR, with 37. It also had the most getting 2+ with 14 and 3+ with 8. If we project forward with rest of 2019 how does it compare with 2015.

Projecting these guys forward for the rest of year isn’t simple but here is my method. There are around 35 games left for most teams and so my projections are based on them hitting the same for another 150 PAs (110 PAs for catchers). Here is what the end of the season fWAR might look like. This is for hitters who already have 100 PA, there are a few like Bo Bichette, Will Smith and Aristides Aquino who don’t meet that criteria but will more than likely end up with 1+ fWAR.
Fernando Tatis Jr.has had his projected PAs brought down to 0 after news of him going on the IL and suggesting that he won’t play again this season.

These projections suggest that 2019 should come close to matching 2015 in all of the records, stated above. Some of these players will get injured and not all of them will get the full playing time so it might not beat 2015. However, there are also players who don’t have 100 PA, who should get to 1 fWAR before the end of the season.

It should be very close to being the best crop in a while, but if it doesn’t it will easily be the second best crop in the last 2 decades.

What stunned me most by this list is that Eloy Jimenez doesn’t make the list and Vlad Guerrero Jr. just makes my 1 WAR prediction list. Who would have thought that at the start of the season, not me for one.

The top hitters is where 2019 looks like it will really shine. The projection has 3 guys with over 4 fWAR and a further 3 with 3.9. To put that into context over the last 21 years, there have been just 30 players who have had rookie season fWAR of 3.9 or better. That is 1.5 per season and I am projecting 6 might do it. I was projecting a 7th until the news about Tatis Jr.

Since 1998, 10 players have had a 5+ fWAR season as a rookie, Pete Alonso projects to break that mark.

It is a pretty amazing list to join, but does a better rookie season suggest a hitter will be better across their career. If so, I think the hyperbole around rookies playing well might not be as hyperbolic as I thought it was.

Looking at the career fWAR for rookies, who get 100+ PA in a rookie season, from 1998 to 2010 it does seem to suggest that the better the rookies season, the more fWAR a hitter might expect to get in their career.

Note: I want to give a mention to Cristian Guzman here, his rookie season in 1999 was worth -3.1 fWAR, two years later he posted a 3.9 season and earned a All-Star appearance. He ended his career with 8.2 fWAR, a far cry from his first season.

This data makes what I thought was hyperbole about rookie hitters, a lot more reasonable. Now let’s look at pitchers, below is bucketed fWAR for rookie pitchers with 40+ innings pitched.

First thing you will notice is that the spread of fWAR for pitchers isn’t as much as for hitters, this most likely due to the allocation of wins in WAR calculations. Current WAR models use a 57/43 split of the 1000 wins between hitters and pitchers.

At the time of writing, there are only 4 rookie starters which have more than 1.5 fWAR. Projecting all starters a further 35 IP for the rest of the season, they are the only 4 which project for 2+ fWAR.

If this happens it will equal the lowest number of 2+ fWAR rookie pitchers in a season since 1998. That being said, Mike Soroka is on course for a top 5, maybe top 3, rookie season.

That list doesn’t have the stars that the hitting list does so should fans be expecting as much from their top rookies in the seasons to come. Below is based off the lifetime fWAR for rookie pitches from 1998 to 2010, who threw 40+ IP in that season.

Compared to hitters with the same fWAR bucket, pitchers are less likely to have 10+ or 20+ WAR careers. However, there is still the correlation between a better rookie season and a better career fWAR.

In conclusion, it does look like we are seeing a uniquely talented crop of rookie hitters coming through this season and fans should be excited about these players future performance. On the other hand, the rookie pitchers have struggled with the real exception of four mentioned especially Mike Soroka.


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