Due to Major League rules, Bannister won't be in uniform during games. But he will be on the field during the pregame hours both at home and on the road.
The Red Sox entered play on Tuesday with a 4.48 ERA, which ranks 22nd out of the 30 Major League teams.
"He's going to assist us, assist in dealing with Carl Willis and helping with our pitching staff," said Red Sox president of baseball operations Dave Dombrowski. "Brian has done an outstanding job for us in many different areas. When he was hired, we really thought he would help us in various areas. But we also thought we would let the position develop over time and use him where needed. We felt at this point that our major focus should be on our Major League pitching staff and trying to help it in any way we possibly can."
Dombrowski said the move was not a reflection of the job Willis has done with the staff.
"It's not that we're unhappy with Carl, but we're looking for any way to make ourselves better," said Dombrowski. "And I don't mean to say, by any means, that you don't try to get better from a talent perspective also, which we will continue to try to do, but there's a lot of work to be done. And we think it maybe gives us a little bit of an edge and will help us improve."
Red Sox pitchers have been receptive to some of the analytics Bannister has collected and can now have more direct access to him.
"We've got a number of pitchers here that have talked to Brian in Spring Training," said manager John Farrell. "They ask for the objective data that he generates. And rather than that be indirect, we felt like his ability to be with us each and every day to assess from a Pitch-f/x standpoint and the information that he provides, to be around us more frequent would help.
"I think you're seeing pitchers become more open-minded to this information and how it allows them to understand when they're at their best from that standpoint rather than a traditional delivery standpoint or what the advanced scouting report information that we provide to help set up an attack plan."
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.