Slugging percentage (SLG) has long been the go-to stat for measuring power-hitting in baseball. The stat is calculated using the total bases a player notches for each hit. SLG can be calculated using the following formulas:
SLG = [ (1B) + (2 * 2B) + (3 * 3B) + (4 * HR) ] / AB
SLG = Total Bases / AB
SLG uses singles as well as extra-base hits in its formula. Isolated Power (ISO), on the other hand, does not. ISO excludes singles from its formula. It isolates extra-base hits—hence the stat's name. Here are the ways to calculate ISO:
ISO = [ (2B) + (2 * 3B) + (3 * HR) ] / AB
ISO = SLG - BA
ISO = Extra Bases / At-Bats
I've previously written about why I prefer to use ISO instead of SLG when evaluating how much power a player has hit for. The TL;DR explanation is that ISO excludes singles from its calculation, so singles can't inflate ISO like they sometimes can SLG.
Derrick Goold of the St. Louis Post-Dispatch touched on Holliday's power in article that was published on stltoday.com last week. In the piece, Goold quoted the Cardinals left fielder:
"It's been frustrating for me from the standpoint that I haven't been able to drive as many balls as I would like," said Holliday, has a career .525 slugging percentage but a .368 figure this season. "I've been rattling my brain for hours trying to figure out exactly what it is. ... I'm just trying to figure out where the problem is and what's causing it and remedy it. I have done a good job of getting on base. The slugging percentage is not something I'm happy with. It's pretty poor."
Since Goold's article with Holliday's quote ran in the Post-Dispatch, Holliday has swatted two homers and three singles, raising his SLG from .368 to .384 and his ISO from .104 to .120. Nonetheless, Holliday's SLG and ISO are both well below his career and typical seasonal levels. In a full season, Holliday has never posted a SLG below .488 (which he did in his rookie season with the Rockies) or an ISO below .190 (last season for the Cards). Entering play Tuesday against the Mets, Holliday's SLG sits 141 points below his career rate; his 2014 ISO is 94 points below his career ISO.
Goold and St. Louis Post-Dispatch columnist Bernie Miklasz discussed Holliday's lacking power on The Best Podcast in Baseball (a weekly must-listen for Cardinals fans) during last week's episode. Goold shared that Holliday's timing was off—at least until he start zeroing in on pitches during the at-bat in Tampa that resulted in his fourth dinger of the season. Perusing the heat maps at the indispensable Brooks Baseball, we get an idea of the problem: Holliday isn't murdering hard pitches (fourseamer, sinkers, and cutters) like he used to.
The following chart shows Holliday's ISO strike zone map against hard pitches from 2007 through 2013.
So far this season, Holliday isn't hitting for as much power against fourseamers, sinkers, and cutters—particularly on pitches in. Holliday has hit for power on hard pitches within the strike zone and inside when they are up and down. However, he hasn't had much luck in terms of power when pitchers bust him in on the hands (both in the zone and off the plate).
Against the Rays last Tuesday, Holliday fouled off several fastballs before depositing an 86-mph splitter beyond the outfield wall for a homer. Facing Doug Fister on Sunday, Holliday ripped a first-pitch fastball over the fence. Pitch F/X clocked the Fister offering at 87 mph. I'll be watching with interest to see whether Holliday is able to rope pitches that clock in the 90s for extra-base hits as the temperatures rise with the onset of summer.