Short answer: Casper Ruud plays the Yonex EZONE 100, strung with a poly-on-poly hybrid: Yonex PolyTour Spin in the mains and PolyTour Pro in the crosses, both at the same tension of 54 to 56 lbs.
The frame
The EZONE 100 is one of the most widely played frames in the world, and for good reason. It is a 100 sq in head with a 16x19 pattern, comfortable, powerful for its class, and forgiving without being a beginner racquet. Ruud is a clay-court specialist by reputation and a heavy topspin player by method, and the EZONE gives him the launch angle to hit with margin over the net.
Published specs
- Head size: 100 sq in
- String pattern: 16x19
- Character: comfortable, powerful, spin-friendly
The hybrid, and the thing worth copying
PolyTour Spin mains, PolyTour Pro crosses, both around 54 to 56 lbs. Spin is a shaped string designed to bite the ball; Pro is smoother and softer. Putting the shaped string in the mains is standard practice, because the mains do most of the work of gripping and releasing.
What makes Ruud unusual is the consistency. He strings both at the same tension and he rarely changes it. No adjusting for conditions, no chasing feel week to week. In a sport full of players tinkering constantly, he found a setup and stopped.
That is worth more attention than the specific strings. Most club players change tension far too often, chasing a result that has more to do with their timing than their string bed. Picking a setup and staying with it long enough to actually learn it is underrated advice, and Ruud is the proof.
What you can actually buy
The EZONE 100 and both PolyTour strings are available. The setup link on this page loads PolyTour Pro, since we are down to a single set of PolyTour Spin in his gauge. If you want the true hybrid, order it and note it and we will string Spin mains with Pro crosses.
Should you play this setup?
This is one of the easiest recommendations on the page. The EZONE 100 suits a huge range of players from solid intermediate upward, and the tension is close to reasonable already. Take 4 to 6 lbs off it and you have a setup most club players would be happy with for a year.
If you play a lot of topspin off the ground, the Spin mains genuinely earn their place. If you mostly want comfort, a full bed of PolyTour Pro is simpler and cheaper.
Sources
Frame and hybrid configuration reported by Perfect Tennis and Yonex's own player listings, with tension corroborated across gear discussion. Tour setups change through a season, so treat this as current rather than fixed.