Two of the four remaining pitchers deserve something between a few sentences and a full post, whereas the other two don't merit much discussion.
Tommy John
Surprisingly, beyond having a revolutionary surgery named after him, there's a case to be made in favor of John's induction. His career numbers are pretty strong: 288 wins, 3.34 ERA, 2245 strikeouts. From 1977-1981 he was as good as any pitcher in baseball, winning 89 games and finishing 2nd in the Cy Young voting twice. He led the league in shutouts three times, and his 6-3 post-season record is pretty impressive as well.
But that's about where it ends for him. Despite the relatively high number of strikeouts, he never whiffed more than 150 batters in a season. And it's fair to say that, for his last six seasons, he was pretty much hanging on. There was just nothing that ever screamed spectacular about him. Plus, baseball-reference.com lists Jim Kaat as the pitcher in baseball history most similar to John. I'd say that's a pretty fair characterization; Kaat was a very good pitcher, like John. He's not a Hall of Famer, and John shouldn't be either.
Lee Smith
The hard part of evaluating Smith's career is that the role of the closer has changed so much in the last 20 years, that we're still in the early stages of figuring out how to identify the elite vs. the very good closer. So the question immediately becomes, how do you evaluate Smith's save numbers?
He's had ten 30 save seasons, and ranks third all-time with 478. Smith finished 802 games (most all-time), and appeared in 1,022 games. He was definitely a power pitcher, striking out almost a batter per inning.
On the flipside, he never seemed to be the dominant reliever in baseball during his career, and given that there are currently just four relief pitchers in the Hall, that may turn out to be a big issue. He won three Reliever of the Year awards, but none until 1991 when he was with the Cardinals. He played for eight different teams, which might turn off a few voters (he did have a reputation of being a bit of a malcontent). And then there were his two post-season appearances, both of which he lost a game and contributed to crushing series losses for his team.
Honestly, I don't know what to do with him. Smith, in a lot of ways, strikes me as a Jeff Reardon that was able to extend his prime for a couple more years. I'm not sure that's good enough. Maybe in time, his numbers will start to look better, but for now I'd leave him out of the Hall.
Jesse Orosco
The all-time leader in games pitched...and that's about it. He was a nice lefty specialist...nice lefty specialists don't make the Hall of Fame.
Dan Plesac
Here's a good way to reduce the membership of the BBWAA. Anyone that votes for Plesac, strip them of their vote. Should not, under any circumstance, get any consideration.
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MLB
hall of fame, tommy john, lee smith, jesse orosco, dan plesac