Prospect of the Day: James Paxton, LHP, Seattle Mariners

The Seattle Mariners promoted pitching prospect James Paxton to the major league roster this week, and he'll make his debut with a start against the Tampa Bay Rays on Saturday. Paxton has been on prospect lists for several years now, with his reputation as a prospect yo-yoing to some extent. Here's a look at what we can expect.

Born in British Columbia, Paxton pitched college baseball at the University of Kentucky. Although he posted an ugly 5.86 ERA as a junior in 2009, his outstanding 115/20 K/BB ratio in 78 innings was more indicative of his potential. Drafted in the supplemental first round by the Blue Jays, Paxton didn't come to terms with Toronto, but feel afoul of the NCAA and lost his college eligibility after Blue Jays president Paul Beeston publicly mentioned direct negotiations with Scott Boras.

Paxton made four starts for independent Grand Prairie of the American Association in the spring of 2010, but didn't look as sharp as scouts expected and fell to Seattle in the fourth round of the draft. It still took until the spring of 2011 for him to sign a contract with the Mariners, but he was effective once on the mound, posting a 2.73 ERA with an 80/30 K/BB in 56 innings for Clinton in the Low-A Midwest League, followed by a 1.85 ERA with a 51/13 K/BB in 39 innings for Double-A Jackson in the Southern League.

He returned to Jackson for 2012, making 21 starts with a 3.05 ERA and a 110/54 K/BB in 106 innings, missing several weeks of action due to a knee injury. He spent all of 2013 with Triple-A Tacoma in the Pacific Coast League, posting a 4.55 ERA with a 131/58 K/BB in 146 innings, allowing 158 hits.

Paxton is a 6-4, 220 pound left-handed hitter and thrower, born November 6, 1988. He has impressive arm strength for a lefty, topping out at 98 MPH on his best days. However, his velocity is very inconsistent, not just from start to start, but from inning to inning within starts. Pacific Coast League observers noted fastballs anywhere between 87 and 97 MPH this season, with movement likewise varying between above average and below average.

In addition to the heat, Paxton offers a curveball, a change-up, and a newly-developed cutter. The curve is the best of these pitches, but like the fastball it varies greatly in quality, anywhere from plus to below average.

On his best days, Paxton can blow through any lineup with a mid-90s heat, a big-breaking curve, and a decent cutter and change to give the hitters a different look. On his worst days, his velocity sags, he lacks command and leaves his pitches too high in the strike zone, and he gets hit hard.

Why the variance? Paxton has a big over-the-top delivery and he has trouble keeping it consistent.

When everything is working, he shows solid command of quality stuff and looks like a future number three starter. For example, he was very successful this past July, making five starts with a 1.80 ERA and a 27/6 K/BB in 35 innings. Three of those starts (July 13, 22, and 27th) were particularly strong, with an 18/0 K/BB in 21 innings. But Paxton lost the touch with his mechanics again in August, posting a 23/19 K/BB in his final 33 innings of work for Tacoma.

So which Paxton will show up for the Mariners in September? The guy who looks like a mid-rotation starter, or the guy who will be lucky to have a career in middle relief? I wish I knew. If he holds to past patterns, we'll probably see both versions. Whatever happens, Paxton has rare arm strength for a southpaw and will get plenty of opportunity to prove himself.