Anthony Rizzo and Ben Zobrist were forced to swap positions (and gloves) for a single play

Joe Maddon has pulled off some pretty unique plays this season for the NL Central champion Cubs -- specifically, doing things like using pitchers as outfielders (and using them on the mound again later).
What transpired during Wednesday's game with the Pirates, however, was another slice of oddness that came as the result of some quirky defensive positioning. With one out and Eric Fryer on first in the bottom of the fourth inning, Jameson Taillon was at the plate looking to sacrifice. Anthony Rizzo was playing in, anticipating the bunt, so second baseman Ben Zobrist was holding Fryer at first base. 
Then, this happened: 

You see, Pirates manager Clint Hurdle notified the umpires that Rizzo and Zobrist had effectively swapped positions, so, per the rules, they'd have to use gloves for their respective new defensive roles. Both obtained new gloves, Zobrist using a first baseman's mitt and Rizzo a left-handed, non-first-baseman's glove. If it sounds confusing, that's because it was. 
Taillon then put down a successful bunt to Rizzo, Fryer advanced to second with two outs, and anyone keeping score had to deal with this:

Then, Zobrist and Rizzo returned to their original, familiar positions and all was well with the universe once again. 
After the game, Maddon explained his side of the situation to MLB.com's Carrie Muskat: 
"It's one of those things we need absolute definition with. I forgot to ask 'Riz' to bring his other glove down to the dugout today, so it's partly my fault. I don't know where the lore has been dictated. There's no actual rule that says you can't do that. It's just interpretation by the crew chief. If they want us to be able to do that, we will. Nobody was upset. Two crews have said no, one crew has said yes. I still don't understand the dispute and why it's a big deal. We'll play good in the sand box. Just tell us what [the rule] is."
He continued:
"The guy closest to first base has to have a first baseman's mitt. That's what they're telling me. My response to that is when [Kris Bryant] goes and plays in the slot in right field [on a shift] and a ground ball is hit to him, how do you score it? 5-3. If a bunt is hit to Rizzo in that little defense and he throws to second base and then to first, how is that scored? 3-6-4 double play. He's still the first baseman. It's all semantics, it's based on interpretation. Give us something to hold onto and we will."
Rizzo, meanwhile, seemed to get a kick out of his new positional turn: 
"I'm going to change that on my Twitter bio -- 'first baseman and second baseman," he told Muskat. 
Hurdle explained his reasoning as follows when speaking with MLB.com's Adam Berry: 
"The only way a first baseman's mitt can be used is by a first baseman. It's in the rulebook. When Rizzo came into the infield, didn't play first base, it's an illegal glove. Then you've got a guy playing first base with a fielder's glove. I asked them about the rules, and he agreed. I guess Gorman was already on it at the same time. Zobrist was on the bag without a first baseman's mitt. The only way you can have a first baseman's mitt is you've got to play first base. Rizzo's in the middle of the diamond with a first baseman's mitt. It's not a legal glove."
Taillon, whose bunt attempt led to all this, told Berry it was a definite first for him: 
"Montero, we were trying to talk through the situation. He's like, 'I think Zobrist might need a first-base glove. I've never seen this get called out before.' I'm like, I've never seen a shift before like that. I guess you see something new every night in this game."