Contextualizing the Pirates’ Minor League Hitting Numbers

When it comes to minor league players, FanGraphs does a solid job of providing standard and advanced stats. Visit their Minor League Leaders page, and you’ll find pages of hitting numbers for players at every level of the minors.

Unfortunately, while the numbers are easy enough to find, they’re not as easy to draw conclusions from. These days, we’re used to numbers being contextualized: adjustments for season and for park and everything in between. When it comes to minor leaguers, though, the numbers are served about as raw as a sashimi tuna roll.

For example, if you look at the advanced tab, you’ll find that Kevin Kramer posted a wRC+ of 141, good enough for third among qualified AAA players and ahead of Christin Stewart, who last season was ranked the Detroit Tigers’ number three prospect by FanGraphs. Not bad, right?

Well, let’s take a closer look and see how those numbers hold up.

Park Adjustment

The first adjustment we need to make is for park factor. (If you’re unfamiliar with park factors, FanGraphs has a good explanation.) Simply put, park factors are a way to adjust a hitter’s performance for the stadium in which they played. The calculation is simple, based purely on runs scored at home and runs scored on the road.

After pulling that data from MiLB’s website (not an easy task), I was able to come up with park factors for AAA and AA teams. (Note: for purposes of this post, we’ll stick to the International and Eastern Leagues, since that is where the Pirates AAA and AA affiliates play.)

International League

TEAM	TM	Raw PF	PF
Durham Bulls	TBR	0.96	0.98
Indianapolis Indians	PIT	0.91	0.96
Lehigh Valley IronPigs	PHI	1.08	1.04
Columbus Clippers	CLE	1.02	1.01
Norfolk Tides	BAL	0.91	0.96
Louisville Bats	CIN	0.93	0.96
Gwinnett Stripers	ATL	1.07	1.04
Scranton/Wilkes-Barre RailRiders	NYY	1.00	1.00
Buffalo Bisons	TOR	1.02	1.01
Toledo Mud Hens	DET	0.95	0.97
Syracuse Chiefs	WSN	0.99	0.99
Pawtucket Red Sox	BOS	1.00	1.00
Charlotte Knights	CHW	1.12	1.06
Rochester Red Wings	MIN	1.00	1.00

Eastern League

TEAM	TM	Raw PF	PF
New Hampshire Fisher Cats	TOR	0.98	0.99
Akron RubberDucks	CLE	0.87	0.93
Bowie Baysox	BAL	1.04	1.02
Erie SeaWolves	DET	1.04	1.02
Harrisburg Senators	WSN	1.00	1.00
Portland Sea Dogs	BOS	0.99	0.99
Altoona Curve	PIT	0.92	0.96
Reading Fightin Phils	PHI	1.07	1.03
Binghamton Rumble Ponies	NYM	0.95	0.97
Trenton Thunder	NYY	0.97	0.99
Hartford Yard Goats	COL	1.09	1.05
Richmond Flying Squirrels	SFG	0.87	0.93

The raw single-season park factor is the first number. Since this is only one year of data, however, and because these things are prone to variance, I’ve also regressed 50% back to the mean of 1.00. I’ll be using the regressed numbers for all calculations.

Now, with park factor taken into account, we can adjust the wRC+ numbers. Here are the numbers for all Pirates AAA hitters with at least 200 plate appearances last season. The adjusted wRC+ is on the right.

I must note here that there’s some slight discrepancies between my original wRC+ numbers and FanGraphs’ numbers. Since they don’t publish their Minor League weights, I used their standard numbers and used an estimate based on a linear model to estimate the wOBA scale.

Name	PA	wRC+	PF wRC+
Kevin Kramer	527	142	147
Kevin Newman	477	116	120
Pablo Reyes	398	118	122
Jordan Luplow	357	136	140
Jose Osuna	342	146	150
Christopher Bostick	327	122	127
Eric Wood	308	130	134
Ryan Lavarnway	303	146	150
Max Moroff	297	110	114
Wyatt Mathisen	282	109	114
Jacob Stallings	278	110	114
Erich Weiss	236	91	96
Jason Martin	234	62	67
Jerrick Suiter	219	68	73

Good news! Kramer’s numbers look even better now. Giddy-up.

Now for AA hitters:

Name	PA	wRC+	PF wRC+
Cole Tucker	589	95	99
Will Craig	549	112	116
Ke’Bryan Hayes	508	131	135
Stephen Alemais	463	94	98
Logan Hill	444	95	99
Jordan George	392	100	104
Bryan Reynolds	383	128	132
Christian Kelley	347	89	93
Jason Martin	289	150	155
Bralin Jackson	219	49	53

The Ke’Bryan Hayes numbers are particularly encouraging.

Luck Adjustment

Let’s take our evaluation one step further. Here, again, are the AAA and AA numbers, but this time with one additional column: batting average on balls in play (BABIP).

Name	PA	wRC+	PF wRC+	BABIP
Kevin Kramer	527	142	147	0.392
Kevin Newman	477	116	120	0.333
Pablo Reyes	398	118	122	0.338
Jordan Luplow	357	136	140	0.336
Jose Osuna	342	146	150	0.353
Christopher Bostick	327	122	127	0.367
Eric Wood	308	130	134	0.335
Ryan Lavarnway	303	146	150	0.338
Max Moroff	297	110	114	0.270
Wyatt Mathisen	282	109	114	0.285
Jacob Stallings	278	110	114	0.343
Erich Weiss	236	91	96	0.289
Jason Martin	234	62	67	0.261
Jerrick Suiter	219	68	73	0.303

And AA:

Name	PA	wRC+	PF wRC+	BABIP
Cole Tucker	589	95	99	0.310
Will Craig	549	112	116	0.288
Ke’Bryan Hayes	508	131	135	0.344
Stephen Alemais	463	94	98	0.326
Logan Hill	444	95	99	0.293
Jordan George	392	100	104	0.293
Bryan Reynolds	383	128	132	0.362
Christian Kelley	347	89	93	0.270
Jason Martin	289	150	155	0.396
Bralin Jackson	219	49	53	0.291

As you can see, BABIP has a rather large influence on the wRC+ outcome. In fact, Kramer nearly hit .400 on balls in play last season! That likely plays a big part in his 142 wRC+.

So what happens to those numbers when we adjust for some measure of “luck”? By adjusting a player’s hits based on league-average BABIP, we can see just how much luck has inflated the raw numbers.

Last season, league-average BABIP in the Major Leagues was .296. In the International League, the average BABIP was .309, while average for the Eastern League was .307. It makes sense that those numbers would be higher for lower levels of baseball given defense and pitching talent discrepancies, though it’s hard to say why the AA level actually produced a lower BABIP number.

Now, after adjusting a player’s singles, doubles, and triples so that their BABIP falls in line with the league average, while maintaining the same ratio, we can recalculate wOBA, wRAA, and, of course, wRC+.

AAA Adjusted wRC+

Name	PA	wRC+	PF wRC+	LUCK wRC+
Kevin Kramer	527	142	147	107
Kevin Newman	477	116	120	104
Pablo Reyes	398	118	122	107
Jordan Luplow	357	136	140	125
Jose Osuna	342	146	150	128
Christopher Bostick	327	122	127	97
Eric Wood	308	130	134	120
Ryan Lavarnway	303	146	150	136
Max Moroff	297	110	114	129
Wyatt Mathisen	282	109	114	126
Jacob Stallings	278	110	114	97
Erich Weiss	236	91	96	105
Jason Martin	234	62	67	92
Jerrick Suiter	219	68	73	71

The luck-adjusted numbers for Kramer now look much more pedestrian. (In case you were wondering, Christin Stewart’s adjusted wRC+ is 147 after adjusting for park and BABIP luck.)

AA Adjusted wRC+

Name	PA	wRC+	PF wRC+	wRC+
Cole Tucker	589	95	99	95
Will Craig	549	112	116	125
Ke’Bryan Hayes	508	131	135	116
Stephen Alemais	463	94	98	89
Logan Hill	444	95	99	108
Jordan George	392	100	104	112
Bryan Reynolds	383	128	132	108
Christian Kelley	347	89	93	112
Jason Martin	289	150	155	117
Bralin Jackson	219	49	53	61

The Hayes numbers look less impressive now, but they offer a brighter outlook for Will Craig. Of course, it’s also worth noting in those comparisons that Craig is two years Hayes’ senior.

In short, while there is plenty of good data out there on baseball prospects, it’s always important to remember just how these numbers look when put into a wider context. A player’s park, as well as their luck, can play a large part in how good or bad they look. And while, over time, player’s may prove higher BABIP numbers are due more to skill than luck, it’s still worth keeping in mind when evaluating prospects.