context: Despite his limited success on the main ATP circuit, Sluiter won 10 ATP Challenger Tour titles during his career.
source: Though a singles specialist, Sluiter was also an occasional doubles player.
reference_original: Obwohl Sluiter Profi im Einzel war, spielte er gelegentlich im Doppel.
reference_flipped: Obwohl Sluiter Profi im Einzel war, spielte sie gelegentlich im Doppel.