Jim Kaat vs Jerry Koosman: Career Stats Comparison
Jim Kaat (1959–1983) and Jerry Koosman (1967–1985) — breaking in during the 1950s and the 1960s respectively, so they pitched against very different hitting environments. Jim Kaat compiled 283 wins and 2,461 strikeouts; Jerry Koosman put up 222 wins and 2,556 strikeouts. The numbers below run them through identical career and rate-stat lenses.
Jerry Koosman
Career Stats Side-by-Side
Every cell below is a career total or career rate. Cells highlighted in green mark the player who leads that line. For pitchers, lower ERA, WHIP, and BB/9 lead; higher K/9 leads.
| Statistic | Jim Kaat | Jerry Koosman |
|---|---|---|
| Wins | 283 | 222 |
| Losses | 237 | 209 |
| Games | 898 | 612 |
| Games Started | 625 | 527 |
| Complete Games | 180 | 140 |
| Shutouts | 31 | 33 |
| Saves | 18 | 17 |
| Strikeouts | 2,461 | 2,556 |
| Walks | 1,083 | 1,198 |
| Hits Allowed | 4,620 | 3,635 |
| Home Runs Allowed | 395 | 290 |
| Innings Pitched | 4,530 | 3,839 |
| ERA | 3.45 | 3.36 |
| WHIP | 1.26 | 1.26 |
| K/9 | 4.89 | 5.99 |
| BB/9 | 2.15 | 2.81 |
PIV Comparison
By PIV (Player Impact Value), Jerry Koosman outpaces Jim Kaat 42,939 to 26,792 — a gap driven primarily by per-season impact (2,147 vs 957 per year). PIV adjusts each season to league baselines, so it's the cleanest way to compare careers across eras.
Peak Seasons
The best single seasons each player produced, ranked by ERA among qualified workloads (120+ innings).
Jim Kaat — top 3 seasons by ERA (lower is better)
Jerry Koosman — top 3 seasons by ERA (lower is better)
Verdict
On the head-to-head card, Jerry Koosman leads in strikeouts, ERA, WHIP, and K/9, while Jim Kaat owns wins and innings pitched. That doesn't settle the era debate, but on the raw scoreboard the edge goes to Jerry Koosman. PIV agrees: Jerry Koosman grades out higher across their careers. Click through to each profile for the full season-by-season breakdown.