Most sports activity trackers are designed rugged so that they will withstand knocks and shocks. They're usually waterproof enough for diving too.
More basic models will have a plastic case and strap, but spend more and you'll get a metal bezel or casing, might get a tougher glass face and may be able to purchase a metal strap too.
If your primary goal is sports tracking beware of flashy features though. We've tested high-end smartwatches that are heavy and uncomfortable to wear, with sharp metal edges that dig into your wrist when holding the bars.