Yah... broke his ankle.
Movie: Sometimes a Great Notion, AKA: Never Give an Inch.
Direction of the film started with Richard A. Colla. Production was halted after 5 weeks to allow Paul Newman to recover from a broken ankle. When film production (shooting) re-started, Richard Colla had quit due to disagreements with Henry Fonda. Paul Newman then took over as film director. Newman was already co-producing the film with John Foreman (his brother Art Newman who was the film's business manager).
As for the question about Paul Newman doing his own tree cutting and topping? Never happened. Good Hollywood editing for those scenes. The logger who did the actual topping of the spar tree was Wayne Bryant. To make it look like Newman did the topping, they found a small hemlock along a logging road and built a platform around the base. Then they notch cut the tree and started the back cut and left a saw stuck in the back cut. Then Paul Newman climbed up the tree with his spurs a few feet above the platform and held the handle of the saw for the close-up shots. The wide angle and pan shots of him sitting on top of that topped tree was really Wayne Bryant.
Hank Stamper on being a logger: "It's one dirty, tough, miserable way to live ... It's about as dangerous a way to make your bacon as you can find."