The landscape of Major League Baseball has rapidly changed in the post-steroid era. The amount of runs scored per games has withered while strikeout rates and fastball velocities skyrocket. One of the most dramatic shifts has been the value teams have placed on young, cost-controlled talent. Teams are now paying ridiculous amounts of money to players under 30-years-old—and with good reason too. Veteran players are just not valued as highly anymore. When the Mariners signed a 34-year-old to a four-year contract worth $57 million last year, it was met with derision and displeasure. But Nelson Cruz surprised all of us when he blasted a career-high 44 home runs and was the only thing standing between the Mariners and a 90-loss season.
By all accounts, Cruz had a career year in 2015. Building upon a very successful one year stint with the Orioles in 2014, Cruz set a new career high in wRC+ (158), and his 4.8 fWAR was his highest mark since 2010. After such a successful year, it’s reasonable to expect some sort of decline in 2016—a combination of age-related decline and simple regression to the mean. The projection systems bear this out. ZiPS calls for a wOBA of .350, a 46 point drop from last year. Steamer is much more pessimistic, seeing a 57 point drop, all the way to .339.
Back in 2013, Jeff Zimmerman published a study of hitter aging curves in the post-steroid era. He found that hitters tend to contribute at their peak right away, and have a steeper decline later in their career.
Age-related decline is a complex process that affects different players in different ways. The curves above show general, league-wide trends. Still, it’s disconcerting to see the sharp cliff batters face in their mid-30s. Cruz will be 35 in 2016 placing him smack dab in middle of that steep decline phase.
To get a better idea of how modern batters are aging, I took a sample of all 34-year-olds who accumulated at least 450 plate appearances between 2006 and 2015. I filtered out players whose wOBA was under .340 to match Cruz’s talent level. The remaining 38 players were then compared against their performance in their age-35 season. On average, these players lost around 15 points of wOBA and 9 points of wRC+. Some of the biggest gains were from players like Victor Martinez and Lance Berkman; the biggest losers were players like Rich Aurilia and Ray Durham.
For his part, Cruz is doing his best to buck the trend. Yes, much of his success last year was driven by an extremely high BABIP, though his line drive rate was higher than ever and his fly ball rate was at a career low. That may not bode well for his ability to hit 40+ home runs in 2016—his 30.3% HR/FB rate is bound to come back down to earth—but there are two underlying stats that may indicate a more gradual decline.
In 2015, Cruz’s average batted ball distance of 307 feet ranked 7th in all of baseball. Even more impressive was the spike in batted ball distance during the second-half of the season.
After the All-Star break, Cruz's average fly ball distance was an unbelievable 333 feet. That led to more than two-fifths of his fly balls leaving the yard in August and September.
This incredible feat of strength was supported by his average exit velocity. A few weeks ago, Craig Edwards showed that batted ball velocity has a relatively high relationship between the first- and second-half of the season. The correlation (the r-squared value) between the two time periods for exit velocity is higher than ISO, which has a quick stabilization point. The data suggests that exit velocity could also have a quick stabilization point as well. As the season wore on, Cruz’s average exit velocity increased by 5.1 mph! His second-half mark of 95.7 mph would have ranked second in all of baseball, just behind Giancarlo Stanton. Not only was Cruz hitting balls farther in the waning days of summer, he was also hitting them harder.
Both Steamer and ZiPS project a significant drop in ISO for Cruz, one of the main reasons why their overall projections are so pessimistic. If his powerful performance in the second-half of the season is any indication of his strength, I have a hard time believing his power numbers will drop so far. The changing batted ball peripherals tell me he may have a year or two left before we see any significant decline. If that’s the case, the four-year deal he signed last year certainly won’t seem as bad as we might have initially believed.