A spinner assembly for an instrument having valves and/or slides. A clamp sub-assembly attaches to the instrument while a hand strap sub-assembly encircles a player's conjoined hand. A bearing rotatably connects the clamp sub-assembly to the hand strap sub-assembly about a drive axis (D) that is offset from the natural balance axis of the instrument (X). The clamp sub-assembly includes a mounting plate fashioned with three side-by-side cradles that nest against the horn valves. A lashing holds the cradles in position. The hand strap sub-assembly includes a generally rigid palm plate that fits in the player's palm. The palm plate has a hypothenar end, a web end and a distal edge. The distal edge has a ring finger relief adjacent the hypothenar end. A driver boss is affixed to the backside of the palm plate adjacent the web end. A flexible belt secures the player's hand to the palm plate.