There's no single set of rules determining who is and is not a "prospect." Some places stick to strict rookie limits, allowing for players signed to major league contracts out of foreign professional leagues (Daisuke Matsuzaka and Masahiro Tanaka, for instance) to stand out like sore thumbs at the top of the charts. Others focus on age, or where the player is expected to start the season.
I won't lie, our definition at Over The Monster has always been vague at best, and taken on a case-by-case basis. Rusney Castillo is not, and in some small part it's because of his age. Mostly, though, it's because he was never intended for the minor leagues outside of a few weeks to get up to speed after a long layoff. If he was 24, perhaps he would be on this list, but probably not. When you're signed to a contract worth more than $70 million and penciled into just about everyone's Opening Day lineup, it's hard to put you on the same list as fresh draft picks.
All this is to say that Steven Wright, #17 on our list, is not your typical prospect for so many reasons. He is as close to 31 as he is to 30, and has spent the last eight years of his life slogging away in the minors to earn just 34 innings in the majors, mostly in unimportant innings or games. He was traded to Boston by the Cleveland Indians for Lars freaking Anderson after the point where Lars Anderson was anything more than an embarrassing reminder of the danger of the prospect hype machine that we're currently fueling because, really, what else are we going to do in February?
Also, he throws a knuckleball, which for the purposes of this conversation is kind of a big deal. It's that knuckleball, adopted only four years ago, that has allowed Wright to erase from the minds of his supporters the first half of his career, leaving behind only three productive seasons--all in the upper-minors--including a 2014 campaign which saw him dramatically lower his walk rate after two years of struggles. It makes his age seem that much less important, given how little the pitch demands of a pitcher physically. And it doesn't hurt that the knuckleball has some positive connotations in Boston thanks to fan-favorite Tim Wakefield.
Of course, the knuckleball has also produced all of two successful pitchers in the last 20 years. And it was as recently as 2008 that we saw Charlie Zink seem to master the pitch in Triple-A Pawtucket (arguably even more so than Wright this season) only to wash out of baseball in within two years.
The reality of the situation is that it's damn hard to say with any certainty where Steven Wright is going to end up. Or, rather, that whatever certainty we have is based less on a firm conviction about Steven Wright himself than a general understanding of what happens with guys like Wright. When it comes to, say, Brian Johnson, he's just never going to be an ace. He might have a good year or two where he's one of the better members of the rotation, but he's never going to be a Clayton Kershaw or a Max Scherzer or anywhere near that. He doesn't have the tools.
With Wright we can say that the chances of him becoming an R.A. Dickey are minuscule. That most knuckleballers are just making a last-ditch attempt to stay in baseball, much less earning Cy Young honors. Hell, given even odds, we would bet everything we own on that not happening. But the possibility isn't quite zero in the way it is with Brian Johnson or any of a million other pitchers like him. Add that to a more plausible (if frankly still unlikely) Tim Wakefield scenario, and it's understandable why, at this point in the list, some would err on the side of the eternal knuckleball hope.