John Smoltz would more than likely go in the Hall of Fame if he just started for the time he did. His 4 seasons as a reliever make his accumulated numbers even better. Smoltz had 17 seasons as a starter, going 207-147, 3.39 in 477 games, 476 starts. He had 2784 Ks in 3187 2/3 IP. As a reliever though, he was dominant for the 4 seasons he was in the pen. He was 6-8, 2.65 with 154 saves in 246 games, 5 starts. The 5 starts came in the first season before he was made the closer. He also had 300 Ks in 285 1/3 IP and had a season where his ERA was 1.12. He also had seasons of 45 and 55 saves and him and Eckersley are the only pitchers in the history of the game with a 20 win and a 50 save season.
Derek Lowe was the only other pitcher in recent memory that had sustained success as both a starter and a reliever. Out of his 16 MLB seasons, he has started for 11 1/2 of them. In 377 games, 364 starts, he is 156-130, 4.15 and has 1382 Ks in 2219 1/3 IP. As a reliever, which covers 4 1/2 seasons, he is 19-27, 86 saves in 295 games, 13 starts. His ERA is better at 3.21, but his strikeout rate is about the same.
Among others worth mentioning is Rick Aguilera, who in 11 1/2 seasons as a reliever was 44-53, 318 saves and a 3.31 ERA in 635 games, 3 starts. He had 635 Ks in 725 1/3 IP. As a starter (4 1/2 seasons), he was 42-28. 3.90 ERA in 97 games, 86 starts. He had 395 Ks in 566 IP.
CJ Wilson pitched his first 5 seasons out of the pen. In 258 games, 6 starts, he was 12-20, 4.30 and 52 saves in 280 2/3IP and 261 Ks. He has become a top of the rotation starting pitcher, going 44-25, 3.35 in 101 games, 101 starts over the past 3 seasons. He has struck out 549 in 629 2/3 IP over that time.
Braden Looper was clearly a better reliever than a starter. He had a full seasons out of the pen, going 34-32, 3.57 with 103 saves for the Marlins, Mets and Cardinals in 572 games, 0 starts. Never a strikeout pitcher, his K rate was higher as a reliever (374 in 607 1/3 IP- 295 in 568 2/3 IP). His final 3 seasons saw him go 38-33, 4.76 in 98 games, 97 starts.
Adam Wainwright had a big impact on the Cardinals in his first season. It was his only year as a reliever, but he went 2-1, 3 saves and 3.12 ERA in 61 games, 0 starts. He had 72 Ks in 75 IP. More importantly, he was lights out in the postseason, going 1-0, 4 saves in 9 games out of the pen. He added 15 strikeouts in 9 2/3 IP. Myers only has the two seasons as a reliever, going 8-15, 4.97 and 40 games in 121 games, 3 starts. Of course, the 3 starts were with the Phillies in 2007 prior to his injury and subsequent move to the back of the bullpen upon his return.
I will conclude this piece with a chart of the before mentioned and games started and relieved, both in the regular season and postseason. Guys like Aroldis Chapman and Neftali Feliz, both getting a chance to dominate as closers, are likely to be starters next season. Feliz started last year, before injuries ruined his season.
Pitcher RSGS RSGR PSGS PSGR
Eckersley 361 710 1 27
Smoltz 482 242 27 14
Lowe 377 295 12 14
Wilson 107 252 9 1
Aguilera 89 643 0 15
Myers 249 128 3 4
Wainwright 151 63 4 9
Looper 97 577 0 15