Possible Clues:

• Novak Djokovic's org
• Org. for netmen
• Tennis tour letters
• Chem. neurotransmitter
• ___ World Tour (sports circuit)
• Org. with a racket in its logo
• Energy-carrying molecule, for short
• Ranking org. for court players
• Roger Federer's org
• Org. for Agassi