How Good is Aaron Hill?


The Arizona Diamondbacks recently continued their busy offseason by extending second baseman Aaron Hill through the 2016 season. The extension itself is worth 35 million dollars over the course of three years, equating to an average annual value of just under $12 million. A contract extension of this short length mitigates much of the risk usually associated with guaranteed-salary baseball contracts, which is particularly important when considering that the deal will keep Hill a Dback through his age 34 campaign. Although Hill is on the wrong side of the aging curve, there is still a great likelihood that this signing will prove to have been a bargain for Arizona when all is said and done.

The Good

Mandatory Credit: Jennifer Stewart-USA TODAY Sports

Aaron Hill is coming off a really, really good 2012 season. How good? Using the fangraphs version of the wins above replacement metric (WAR), only Robinson Cano had a better 2012 as a second baseman. For the uninitiated, WAR takes into account hitting, baserunning, and fielding and is adjusted for postion, league, park, and year in order to determine a single number representative of that player’s value. WAR isn’t perfect, but if nothing else, it gives one a general idea of a player’s overall ability relative to others. Aside from the Yankees’ Robinson Cano and the Rays’ Ben Zobrist, no second baseman was close to Hill’s WAR rating last year. But instead of focusing only on one broad metric, let’s examine Hill piece by piece.

Hill’s most valuable attribute is no doubt his bat. This past year, Hill’s slash line (avg/obp/slg) was .302/.360/.522, compared to a major league average slash line for second basemen of .253/.315/.374. Now, it should be noted that Hill posted those numbers while playing his home games at Chase Field, a hitter’s park. Having said that, Hill’s offensive numbers last season were so above and beyond the major league average for second basemen that the benefit of Chase Field shouldn’t be held against him much at all.

When a hitter sees such a drastic increase in his numbers, often times the change can be attributed to that hitter being particularly lucky that year. With Hill, there are certain indicators of a moderate amount of luck in his 2012 numbers, but nothing to suggest anything extreme. One way in which hitters can be considered “lucky” is by having a high percentage of the balls they put into play fall in for hits as opposed to being caught for outs, this is measured using BABIP (Batting Average on Balls In Play). Last year, Hill posted a .317 BABIP as opposed to his career average of .290 and last year’s major league average of .297. The disparity suggests that we might see Hill’s average dip from the .302 mark he posted this past season, but a slight drop in batting average shouldn’t hurt Hill’s value to any significant extent.

So Hill’s average may have been slightly inflated, but can the same be said of his on-base and slugging percentages?

Aaron Hill’s .360 OBP last year was the highest of his eight year major league career. His OBP certainly benefited to some extent from Hill’s good fortune on balls in play, but there is another reason for the spike. Namely, Hill put up the second best walk rate of his career.

A better eye at the plate last season for Hill shouldn’t be immediately disregarded as completely random, as players do tend to improve their plate discipline with experience. Additionally, Hill was intentionally walked seven times last year, nearly as many as he received in his 7 prior years of major league service combined. It’s difficult to speculate as to why Hill saw so many intentional walks, and whether this year’s lineup construction will present the same opportunities, but regardless, the increase cannot be said to be completely unrelated to Hill’s overall offensive improvement in general. While luck may have influenced Hill’s OBP last year to a certain extent, a good deal of the improvement can be linked to his improved plate discipline, and therefore, ability to draw walks.

While putting up career highs in AVG and OBP, Hill also slugged a career high .522 in 2012. Despite last year only being tied for his second best season to date as far as homeruns, Hill outperformed his previous best slugging percentage by over twenty percentage points. It is likely that Hill’s impressive slugging percentage was due, in part, to playing half his games in hitter friendly Chase Field. The good news for the Diamondbacks in this regard, though, is that he will continuing doing so throughout the length of his new extension.

In addition to park factors, there are various other reasons why Aaron Hill set a new career best in slugging last year. For one, Hill hit flyballs at a rate above his career average. Generally, when a player hits more flyballs in general, he also hits more homeruns as a result. In addition to hitting a greater quantity of flyballs, a higher percentage of those balls Hill was putting into the air were going for homeruns as well. Also, according to the ESPN Home Run Tracker, only four of Hill’s homeruns were of the “just enough” classification, meaning the vast majority of his homeruns were legitimate blasts. Whether it was due to a change of approach or some other factor, Aaron Hill hit more flyballs last year for longer distances, and his slugging percentage reaped the benefits.

The Bad

Mandatory Credit: Jennifer Hilderbrand-USA TODAY Sports

Thus far in the analysis, there has been a whole lot to like about Hill. Thus far in the analysis, however, only Hill’s 2012 season has been under consideration. While it’s true that a player’s most recent season should receive the most weight during analysis, the seasons preceding it must still be considered in the evaluation to paint an accurate picture of who a player really is.

Going by wins above replacement, Hill was a below league-average player in both 2010 and 2011. Needless to say, below league average is a steep dropoff from the position of second best second baseman in the majors. Because WAR includes defense and baserunning, it’s important to check there to see if either of those factored into the poor performances. In Hill’s case, they did not factor in, to any meaningful extent. Aaron Hill was a below league average player in 2010 and 2011 because of his bat.

So we’ve been informed that Aaron Hill put up extremely poor offensive numbers in 2010 and 2011, but why? Those two consecutive off-years were sandwiched by the two best seasons of his career, after all. The situation seems somewhat strange, so let’s take a closer look.

2010 saw Hill post a slash line of .205/.271/.394, a far cry from the career highs he recently posted in 2012. However, the subpar numbers were not entirely Hill’s fault. In fact, Hill was severely unlucky in 2010. That season saw Hill post a BABIP of .196, about 100 percentage points below both league average and his career average. The extremely low BABIP was largely a product of Hill hitting line drives at about half the rate of his career average (10.6% as opposed to 19.2% for his career). Neither number, the BABIP nor the LD%, can be sustained at a rate so low, so Hill’s performance that year could be said not only to have been poor overall, but also extremely unlucky.

In 2011, there was more bad luck for Hill, but it came in a different fashion. His BABIP returned to a level closer to his career average, and his line drive rate actually climbed above his career average. This time, the abberation was his HR/FB rate. HR/FB measures the percentage of fly balls hit that leave the park for homeruns versus ones that remain inside the fence. For his career, Aaron Hill has hit 8.4% of his flyballs for homeruns. In 2011, it was exactly half that number. Because only 4.2% of Hill’s flyballs left the park, naturally he saw a steep dropoff in power that season. As a result, though Hill’s batting average and on-base percentage were far better than they were in 2010, his slugging percentage was substantially lower. His homerun total dropped from 26 in 138 games in 2010 to 8 in 137 games in 2011.

Though hitters do influence their HR/FB via their strength, swing plane, etc., there is certainly still a decent amount of luck that factors into it. Hill likely had a mechanical or approach issue that negatively influenced his homerun rate, but it is likely that there was also a substantial amount of bad luck at play. As with his 2010 effort, Hill’s 2011 performance was not nearly as poor as it would initially seem.

The Outlook

September 25, 2012; San Francisco, CA, USA

The story told by the snapshot of the previous few years of Hill’s career is one full of intrigue. Great 2012 and 2009 campaigns were sandwiched around very disappointing 2010 and 2011 efforts. So is Hill the elite player he was during the highs, or is he the below league average player he was during the lows? The answer is likely somewhere in the middle, but he is certainly closer to elite status than the contrary.

There was far more bad luck fueling Hill’s down years than there was good luck fueling his career year this past season. In the immediate future, with a little luck, Hill can be close to the player he was in 2012. As with all players, though, expect Hill’s performance to begin to decline as he advances closer to his mid-30’s. Still, even if Hill manages to be half as valuable of a player going forward as he was this past year, the new three year extension is a fantastic deal for the Diamondbacks.