Break A Leg: a thread. I found this wee (5 mm) juvenile jumping spider (Phidippus sp., audax or adumbratus) in my garden nomming a fly. Two reasons to zoom in: one, you can see the spider's eyes through the window in the fly wing; and two, the spider only has 2 right legs. And--

--from above, you can see it's also missing a left leg. This isn't uncommon; it's tough out there for a bug, predator or prey. Many arthropods can lose appendages as an escape method, like lizards that can shed their tails. It's called autotomy ("self"+"cut"), and happens at--

--pre-determined break points that then quickly close off blood flow to minimize damage from the injury. And like lizards that re-grow their tails, arthropods can regenerate broken parts, as long as they're still actively growing and molting. So this young spider will probably--

--regrow its limbs over the next couple of molts. Here's a photo of a spider that's successfully done just that. Note the palps (short leg-like appendages on either side of its fangs); the striped one on the right is original, the translucent one on the left is recently regrown.

As for the spider in my garden, I don't know how it lost 3 legs - maybe in a tangle with another spider, or from prey that fought back, or maybe it even survived a parasitic wasp attack (not as likely, but a friend of mine knows of 2 tarantulas that eventually recovered after--

--being paralyzed by tarantula hawk wasps that abandoned the spider before laying eggs). Spider wasps sometimes remove a spider's legs after paralyzing it with a sting (easier transport, or maybe the legs just don't have enough meat to bother with?), as in this next pic of--

--a very unlucky (paralyzed but alive) spider. I don't know for sure, but it looks to me as if the legs have been removed at the handy "break points"; removing the legs in this way would keep the spider from "bleeding out" and thus keep it fresh for baby wasp to eat. Finally--

--here's a terrific article about autotomy, especially in captive tarantulas, by @BugQuestions (which is a great arthropod follow, as are the awesome folks that make up "Ask An Entomologist," @Ms_Mars, @SciBugs, and this article's author, @Stylopidae) https://askentomologists.com/2015/04/13/when-a-spider-loses-a-leg-does-its-whole-hydraulic-system-lose-pressure/