MINNEAPOLIS—Tyler Robertson once stood as the Twins' top lefthanded pitching prospect, a live arm on a 6-foot-5 frame who scouts figured would one day churn out strikeouts.
They compared Robertson, a Twins third-round pick in 2006, with the previous year's third-rounder, Brian Duensing. Both topped out at about 90 mph, relying more on a strong mix of secondary pitches and their own doggedness to retire hitters.
After going 9-5, 2.29 in 16 starts for low Class A Beloit at age 19 in 2007, Robertson climbed to No. 4 on the Twins prospect list, and a consensus grew that he would eventually surpass his fellow third-round lefty.
Things haven't played out that way.
Duensing has settled in as a mainstay in the Twins' rotation. Robertson's career, meanwhile, has stalled after a bout of tendnitis two seasons ago. His strikeouts per nine innings rate atrophied from 10.8 in '07 to 5.7 for Double-A New Britain this season.
"His stuff is still good—his curveball is a great pitch—but he's had a tough time," farm director Jim Rantz said of Robertson's 4-14, 5.41 campaign. "We've been giving some thought into how he might help us."
The new plan: Send Robertson to the Arizona Fall League and convert him to a reliever.
"We're extremely short on lefthanded bullpen guys, especially in our upper levels," Rantz said, "and we think this might be a way he can help the big club."
"Getting him some innings out there will give us a good look at how well he can adapt."
Robertson becomes eligible for the Rule 5 draft in December, so the Twins need to decide whether to put him on the 40-man roster this fall.
"We want to see if his velocity increases," Rantz said, "if he throws more strikes. It might be a way to get his career going again."
• The Twins called on righthander Matt Fox to make an emergency start on Sept. 3, but despite allowing two runs on four hits in 5 2/3 innings, Minnesota deemed him the odd man out after adding Ben Revere to its 40-man roster. The Red Sox subsequently claimed Fox on waivers.
• First-round righthander Alex Wimmers, who logged 16 innings for high Class A Fort Myers after signing out of Ohio State, will pitch in instructional league to increase his innings count.