Through his age-25 season with the Cardinals, Jason Heyward established himself as a hitter who could get on base (.352 career on-base percentage) and show occasional power (97 home runs in 3,480 career plate appearances).
The natural question is whether Heyward as a Cub can show a power surge. At 26, he’s at a normal age for a breakthrough, though some have suggested his track record is long enough for us to know what kind of player he is.
Nine players in the expansion era (starting in 1961) have had at least 3,000 plate appearances, between 75 and 125 career homers and no season with 30 or more homers through age 25. They include current 26-year-olds Heyward, Freddie Freeman and Eric Hosmer.
That leaves six players to explore:
Decline after 25: Cesar Cedeno’s best seasons were early, with 121 homers in 4,126 plate appearances for the Astros through age 25 beginning in 1970. He hit only 78 homers after that.
On the edge: Rusty Staub’s real breakthrough came at age 25, when he hit 29 homers for the 1969 Expos. He topped that with 30 in 1970 and hit 206 from age 26 onward after hitting only 57 in six seasons before the breakout.
Mini-surges: Lloyd Moseby and Ted Simmons had their biggest home-run seasons after 25. Moseby totaled 81 homers with a high of 18 through age 25, moved up to 21 at 26 and to 26 at 27 but never hit more than 14 again. Simmons’ career best had been 20 homers until his best power run with seasons of 21, 22, 26, 21, 14 and 23 began at age 27.
Consistent threat: Ivan Rodriguez had 88 homers with a high of 20 for the Rangers through age 25. For the rest of his 20s, he was a solid power source, with 108 homers from 26 through 29. The big breakthrough came with 35 at age 27.
Dream scene: After hitting 79 homers in 3,247 plate appearances through age 25 and 16 at 26, Carl Yastrzemski became more than the Red Sox could have hoped. With 44 homers at 27 in 1967 and two more 40-homer seasons, he finished with 452.
Expecting a Yaz-like breakthrough for Heyward would be a bit much. Still, Yaz, Moseby, Simmons and Rodriguez have shown upswings happen after 25, even for experienced players.
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