Basically, similarity scores compare players to players from the past. Leake turned 28 after the 2015 season. So his similarity score is to that of other pitchers through their own age-27 seasons. The pitcher Leake is most-similar to is Dan Haren, the former Cardinal. Second on the list? Yep, it’s Lackey.

So in a way, you can say that the Cardinals replaced the 37-year-old John Lackey with a 28-year-old “John Lackey.”

Earned run average is only an aspect of the similarity score, sure. But it’s a recognizable gauge. And check it out – in his first six seasons, Leake’s ERA was 3.88. In Lackey’s first six seasons, Lackey’s ERA was 3.82.

And while much will be made of Lackey on the rival Cubs this season, the reality is: The Cards themselves didn’t make a major push to bring him back. Instead, they locked in Leake for his late 20s and early 30s.