Here's what the Rangers do know: Jennings has been their best relief pitcher through the first seven games of the season. That's a short sample, but going into Tuesday, Jennings had pitched 3 1/3 innings without giving up an earned run. He had allowed two hits and two walks while striking out six.
He is also doing it late in the game. Jennings has entered a game twice with two outs in the sixth and once to start the seventh. That's more like the role of a setup reliever, rather than the middle/long relief role they initially envisioned for him.
It appears that Jennings will fill the role that the Rangers originally planned for Brendan Donnelly and/or Derrick Turnbow in the spring. It's a role once filled by Joaquin Benoit before he got hurt and Frank Francisco before he ascended to the closer's role.
It's a physically demanding role and requires being able to pitch back-to-back nights. Jamey Wright pitched back-to-back nights on 15 different occasions last year, plus one stretch where he pitched in four consecutive games. The Rangers have yet to go back-to-back with Jennings.
"The way he's throwing the ball, it depends on if he recovers," manager Ron Washington said. "So far it's been pretty good but we haven't had a need for him to go back-to-back."
Jennings' health is the issue. He has had two major surgeries to repair a torn flexor tendon in his right elbow over the past two years and the Rangers want to be careful they don't put him in jeopardy.
"We have to be sensitive of that," Washington said.
The Rangers weren't even sure about using Jennings in the bullpen in the first place. The idea was treated with some reluctance in Spring Training until it was clear that he could handle the role and that the Rangers needed him in that role.
That need hasn't lessened in the first week or so of the season. If anything, it has increased. Rangers relievers, even though Jennings had not given up an earned run, had a combined 8.02 ERA going into Tuesday's game. The other three right-handed setup candidates -- Warner Madrigal, Josh Rupe and Scott Feldman -- had allowed 14 runs in 9 1/3 innings.
"They're still telling me to be ready in the first and in the ninth," Jennings said. "I'm trying to be ready all the time. They put me in different situations in the spring, so I'm used to it so far. But it's all so new to me, I don't really know what to expect. I'm just happy to be healthy and be a part of the team. Any role is welcome. We'll just see how it plays out."