A mower cutting unit is provided with a rear-mounted grass catcher. The cutting unit includes front and rear rollers and mounted between the rear roller and the grass catcher is a rotary brush. The brush is mounted for adjustment into and away from engagement with the rear roller and for adjustment into and away from engagement with the turf. The brush may be driven either in the same direction as or counter to the direction of rotation of the rear roller during forward mowing operation. When driven counter to the direction as the rear roller, the brush may either be positioned for only cleaning clippings from the rear roller and depositing them into the grass catcher or be positioned for additionally sweeping the turf. When the brush is driven in the same direction of rotation as the rear roller, it operates, depending on its positional relationship to the rear roller and turf, to either only clean the rear roller, to clean the rear roller while sweeping the turf to disperse clippings or to just sweep the turf to disperse clippings.