Is Fernando Tatis Jr.'s Hot Start a Flash in the Pan?

The Padres’ highly anticipated farm system star, Fernando Tatis Jr., was ranked second among all league prospects before this season, trailing only Vladimir Guerrero Jr., who is considered a hitting phenom. These two top-ranked prospects were subsequently called up to the major leagues. Half a season has passed, and Fernando Tatis Jr. has delivered an exceptionally high-level performance. In just 66 games, he has hit 16 home runs, driven in 41 runs, and stolen 14 bases, with a slash line of .331/.392/.599 and an impressive wRC+ of 154. Among all players with over 250 plate appearances in the league, Tatis Jr.’s wRC+ ranks fifth, with only current MLB monster hitters ahead of him (Figure 1). At this rate, he definitely has a chance to challenge for 30+ home runs and 20+ stolen bases by the end of the season.

Figure 1

Is Tatis Jr.’s Performance Sustainable?

However, those familiar with advanced statistics might notice that Fernando Tatis Jr.’s underlying metrics are not particularly impressive; in fact, he could be considered one of the luckiest hitters in MLB.

Understanding BABIP: The Luck Factor

Let’s first introduce a statistic called BABIP. BABIP stands for Batting average on balls put into play. Simply put, it’s the probability of a ball hit into play becoming a hit, excluding home runs.

The concept behind advanced statistics suggests that in a pitcher-hitter matchup, the only outcomes that truly reflect a player’s skill are home runs or strikeouts. If a ball is merely hit into play without becoming a home run, then whether it becomes a hit largely depends on luck. Therefore, BABIP, which calculates the probability of a non-home run ball hit into play becoming a hit, is generally considered a measure of a hitter’s or pitcher’s luck.

For a pitcher, a higher BABIP indicates worse luck, meaning balls hit into play against them frequently turn into hits.

For a hitter, a higher BABIP indicates better luck, meaning balls hit into play by them frequently turn into hits.

According to Fangraphs data, among hitters with over 250 plate appearances, guess who has the highest BABIP? Fernando Tatis Jr., who leads the league with a .421 BABIP (Figure 2).

Figure 2

Besides BABIP, Fernando Tatis Jr. also leads the league in two other statistics:

1. BA-xBA (Actual Batting Average - Expected Batting Average)
2. wOBA-xWOBA (Actual Weighted On-base Average - Expected Weighted On-base Average)

This means that for both batting average and weighted on-base average, Fernando Tatis Jr. has performed significantly better than what models predicted. However, the calculation methods for xBA and xWOBA are more complex, so we won’t discuss them for now. Let’s first look at the BABIP statistic: can BABIP alone fully explain a player’s luck?

Beyond Luck: What Else Influences BABIP?

Let’s revisit the definition of BABIP: the probability of a ball hit into play becoming a hit, excluding home runs.

Can this definition be equated to a luck index? The answer is no.

From a hitter’s perspective, whether a ball hit into play becomes a hit is not solely determined by luck. Hitters can influence the probability of a hit in three ways:

1. Exit velocity and launch angle: High exit velocity combined with a certain launch angle makes for difficult-to-defend balls.
2. Batting skill: The ability to direct the ball to areas where no defenders are positioned.
3. Running speed: A weakly hit ground ball might result in an infield single.

These three aspects are the blind spots when we use BABIP to measure luck. Therefore, let’s examine Fernando Tatis Jr.’s performance in each of these areas.

Tatis Jr.’s Underlying Metrics

First, let’s look at exit velocity and launch angle. These two metrics can be combined into a single comprehensive indicator: Barrel%. A ‘barrel’ is defined as a batted ball with an optimal combination of exit velocity and launch angle that typically results in a minimum .500 batting average and 1.500 slugging percentage (Figure 3). Barrel% is simply the number of barrels divided by batted ball events.

We can see that among 323 hitters with over 100 batted ball events, Fernando Tatis Jr.’s Barrel% ranks 42nd, which is a respectable performance, but it doesn’t seem high enough to fully explain his elevated BABIP.

Figure 4

Second is batting skill, which is actually harder to quantify because we cannot track the defensive alignment and ball landing spot for every plate appearance. However, we can try to indirectly infer Fernando Tatis Jr.’s batting skill by looking at his spray chart distribution and whether his pull/center/opposite field rates are balanced. According to Table 1, Fernando Tatis Jr.’s pull rate is slightly higher than the league average, suggesting that he might not have complete control over the ball’s direction, thus failing to confirm strong batting skill.

Table 1: Fernando Tatis Jr.’s Pull/Center/Opposite Field Rates Compared to League Average

Third is running speed, but more precisely, what affects BABIP is the probability of an infield hit. Therefore, I directly looked up the infield hit rate (infield hits / ground balls) for all players with over 250 plate appearances in the league. Fernando Tatis Jr. ranks second with an infield hit rate of 14.4% (Figure 6). This high infield hit rate likely contributes to his elevated BABIP, making us perceive him as very lucky.

Figure 6

Statistical Analysis of BABIP Factors

To confirm my hypothesis, I used Excel’s data analysis function to perform a multivariate regression analysis on the aforementioned variables that influence BABIP. Since I couldn’t find a clear quantitative metric for batting skill, I only analyzed the correlation between Barrel%, infield hit rate, and BABIP. Below are the results of my analysis. Since the focus here isn’t statistics, those uninterested can skip the next two figures XD.

Figure 7: Although the R-squared of this model is not large, the P-value for infield hit rate is very small, indicating that infield hit rate can explain some of the BABIP variance.

Figure 8: Based on Figure 7, because the P-value for Barrel% was too large, Barrel% was removed from the regression model, leaving only infield hit rate as a variable, resulting in Figure 8. Although the correlation coefficient is not high, there is a trend where higher infield hit rates correspond to higher BABIPs.

Conclusion: A Look Ahead

In simple terms, the analysis results show that Barrel% has almost no relationship with BABIP (P-value as high as 0.4636); however, infield hit rate is very likely related to BABIP (P-value < 0.001). Therefore, a hitter’s infield hit rate can indeed influence BABIP.

In summary, while Fernando Tatis Jr.’s high BABIP is partly due to luck, his speed might explain some of it. However, the author still believes that Fernando Tatis Jr.’s performance is likely to decline, partly due to his exceptionally high HR/FB (home run per fly ball rate, Table 2).

Table 1: Fernando Tatis Jr.’s HR/FB Compared to MLB Average

Fernando Tatis Jr.’s exit velocity is below league average, and his Hard-hit rate is only around the league average. Given ordinary batted ball quality, such a high HR/FB is quite unusual, suggesting that luck plays a larger role. Additionally, his elevated strikeout rate will be a future concern for this Padres’ top prospect. However, hitting won’t be this rising star’s only value. Fernando Tatis Jr.’s numerous spectacular defensive plays and precise base-running instincts have brought new hope to the Padres, who have consistently finished at the bottom of the NL West in recent years.

Finally, here’s an impressive infield sacrifice fly that stuck with me XD

Video Source: MLB Official Website Data Sources: Fangraphs, https://baseballsavant.mlb.com, MLB Official Website Cover Photo Source: Associated Press