(Photo by Al Bello/Getty Images)

In the sixth inning of Sunday’s 2-1 victory, a sight in the Nationals’ bullpen caused a double take. Wednesday’s scheduled starter Tanner Roark climbed a mound and warmed up. Three days after he beat the Mets, Roark did not enter the game. But, Manager Matt Williams said, he could have.

“He was available,” Williams said. “Light side in the pen to get a feel. If we had to use him late, we’d use him late.”

And what, exactly, made Roark available to pitch in relief between starts?

“We can answer that question on Tuesday,” Williams said.

Williams presumably has good reason for the evasiveness, but it forces speculation. Barring some well-hidden secret, Roark’s Sunday availability stemmed from two possibilities. One, the Nationals believed Roark just needed extra work between starts because of Monday’s off day.

Two, the Nationals may intend to swap Roark and Jordan Zimmermann in the rotation. Currently, Roark is scheduled to pitch Wednesday and Zimmermann is down for Thursday.

Zimmermann pitched  the home opener Friday, so he would be on a five-day schedule to pitch again Wednesday, again thanks to Monday’s day off. If the Nationals wanted to move Roark back to Thursday, he could probably use some action in six days without starting.

By switching Roark and Zimmermann, the Nationals would return to their original alignment. Roark replaced Zimmerman on Thursday in New York after Zimmermann came down with a nasty flu the night before.