You hear wheels before you see them. A skateboard appears around the corner, your dog fixes on it and barks. The rider needs a clear path, and your dog needs space. Neither needs an on-the-spot lesson.
Move off the path if you can, or turn away while keeping the lead secure. Don't step into traffic or pull your dog toward the rider. A parked car, broad verge, or side street can give you a visual break. If the path is narrow and skateboards appear without warning, pick a different route for now.
Practice where you can choose the distance
Ask a helper to move a skateboard slowly at a distance, in a safe open area away from roads and other users. Begin with the board still on the ground. Reward your dog for noticing it while staying loose enough to eat and turn toward you. Next, try a little movement. If your dog stiffens, stares, or barks, the movement or distance is too hard, take a break and restart easier.
You can teach a "this way" turn away from skateboards first, at home and on quiet walks. Use it early, before the wheels get close. Many walks will remain management walks, that is fine. A calm turn can be a more realistic goal than holding a perfect sit beside a fast-moving board.
The movement, sound, or novelty may each matter differently to your dog. Work on only one piece at a time and don't ask a stranger riding past to slow down for your practice. If your dog has pulled you over, redirected onto you, or might reach a rider, ask a qualified, reward-based behavior professional to help make a safety plan. A veterinary check is sensible when reactivity is sudden or broader than this one trigger. For a longer plan around triggers on walks, see the walk reactivity guide, make space for riders and choose a safer route when needed
Sources: Dogs Trust: How to stop your dog chasing cars, bikes and animals. Dogs Trust: How to understand your dog's body language.