Top 10 shortstops in MLB; a look at the free-agent SP market

Houston's Carlos Correa and San Francisco's Brandon Crawford are 1 and 2, respectively, in Buster's shortstop rankings. USA TODAY Sports, AP Photo

The aging process seemed to be suspended during the steroid era, with players performing well into their late 30s and even past their 40th birthdays. But in this era of analytics, there is an increasing age bias, with some executives seemingly leaning on a mantra once popular in the '60s: Don't trust anyone over 30.

The Boston Red Sox lowballed Jon Lester in their negotiations with him, all the way up to the moment he signed with the Chicago Cubs, because of what the metrics told them about investing in older pitchers. Rival executives thought the Los Angeles Angels' signing of Albert Pujols was insanity, because the team bet on Pujols sustaining his production far beyond a player's typical peak years.

But the most recent application of ageism appears to be centered on defense, as the analysis improves and teams learn more about measuring a player's glove work. There is a new working theory for some clubs that in general, the defensive skill of players -- rooted in their range and reaction time -- begins to inevitably decline when the players hit their late 20s. Some evaluators believe this happens earlier than in hitting or pitching because hitters or pitchers can more ably overcome, for a few years anyway, any lost physical skills through the knowledge and experience they've gained.

If a player's primary value is rooted in his defense, some executives believe, you better not count on him holding that excellence into his early 30s or mid-30s.

Andrelton Simmons might be the best working test of this theory, because defense is the backbone of what he provides. He is 26 years old, and he is the best defensive player at the most important position in the field. But already one of the key metrics indicates his best days as a defender might be behind him (more on that below).

This is something to consider in Part 6 of our positional rankings; today we have the 10 best shortstops.

1. Carlos Correa, Houston Astros

Carlos Correa He just turned 21 years old and has played only 99 games in the big leagues, and placing him at the head of this distinguished list of shortstops feels aggressive. But the overwhelming response of evaluators who offered opinions for these rankings is that Correa already is the best overall player at this position. "He's a clone of Alex Rodriguez when [A-Rod] was with the Mariners," said one evaluator. "The size, the power, everything."

Rodriguez won a batting title in his age-20 season, setting a high bar for Correa (and others), but Correa quickly became the most important player in the Houston lineup, with 22 doubles and 22 homers in those 99 games. He scored 52 runs, drove in 68 and stole 14 bases, and despite the fact that wasn't called up until June, he still finished fourth among all shortstops in wins above replacement (WAR).

Within a few years, one executive said, "the conversation about who is the best player in baseball will include three names: [Mike] Trout, [Bryce] Harper and Correa."

2. Brandon Crawford, San Francisco Giants