I just read a comment by a poster named auclairkeithbc at Minor League Ball, and wanted to share it with the posters here on the Snakepit. It seems like sometimes fans like us get frustrated when someone identifies a given pitcher as a No. 1 or No. 2 Starter, or front of the rotation vs. back-end of the rotation starter. Jim previously posted an article divvying up the league into five blocks of pitchers, and found what the range of ERA's relative to each block was. While this is, of course, one way of thinking about No. 1 vs. No. 2 vs. No. 3 vs. No. 4 vs. No. 5 Starters, I have to stress that this is not what the industry considers when it's identifying a pitcher as such.

See the below comment from auclairkeithbc:

No. 1 Starter: Two plus pitches, average third pitch, plus-plus command, plus makeup

No. 2 Starter: Two plus pitches, average third pitch, average command, average makeup

No. 3 Starter: One plus pitch, two average pitches, average command, average makeup

No. 4 & No. 5 Starters: Average velocity, consistent breaking ball, decent changeup, command of two of the pitches

The other more qualitative definition people use quite a bit would be that a No. 1 Starter is someone you’d feel confident about pitching in Game 1 of a playoff series, No. 2 for Game 2, No. 3 for Game 3, No. 4 for an occasional playoff start if necessary, and No. 5 never in the playoffs.

These definitions were not made up on the spot by the poster, but are straight out of the Baseball America Prospect Handbook.

Both the scouting standard and qualitative standard are somewhat subject to adjustment. So for instance, if you have one plus pitch, two average pitches, and plus-plus command, then maybe you could consider him to be a No. 2 Starter. For instance, this is what I call Ian Kennedy syndrome. He has one plus pitch at best (this is being pretty generous to him) but he's been able to pitch like a No. 2 Starter because of incredible command this year, something that definitely wasn't as present last year. On the other hand, you can have two plus pitches, an average third pitch, and below average command, and that might drop you down to No. 3 Starter status. This is what I call Daniel Hudson syndrome. Or I mean, you can just also believe that Dan Hudson's fastball hasn't been a plus pitch, the way it was last year, and that has dropped him down to a No. 3 Starter status. Then, there's the problem when you have a guy like Trevor Bauer, and he throws six different pitches, all of which are at least average or better. How do you fit him into a category?

Anyway, the purpose of this fanpost wasn't to really inspire a debate about the usefulness of this form of categorization, versus any other type of categorization of starting pitchers in baseball. It was simply to provide information on what the industry classification was based on, so that when people read in a news article, that a scout was quoted as saying "Trevor Bauer would be a No. 2 Starter in the majors right now", we know that the scout doesn't mean he expects any specific ERA/FIP/xFIP or WAR out of Trevor Bauer....but that he basically views Trevor Bauer as having two major-league ready plus pitches (in this case, probably the fastball and curveball would be considered plus pitches) and average command.