The Ohio State-Michigan rivalry is heating up off the field, too.

During a Big Ten coaches conference call on Monday, Wolverines head coach Jim Harbaugh accused Buckeyes head coach Ryan Day of breaking on-field instruction rules, according to Mark Schlabach of ESPN.

Harbaugh questioned Day about a photo that apparently shows Ohio State assistant Al Washington working with Buckeyes linebackers, Schlabach adds. Under NCAA rules, on-field instruction isn't permitted until Friday.