Every Legionaire a slinger?

Apr 2018
The suggestion that knights/other soldiers learn how to use a sling continues to show up quite a bit throughout the middle ages for instance in the King's Mirror. However the sense i get is that the primary purpose was perhaps more to just provide a more "complete" training regimen and help improve fitness and dexterity alongside exercises such as running, vaulting, swimming, riding, reading and writing, throwing stones of various sizes, and practicing with a wide variety of different weapons. I don't think they were expecting to actually use slings on the battlefield very often.

Perhaps they occasionally saw use in situations like sieges or skirmishes. For instance if a small party of legionaries was out foraging and got attacked by a number of lightly equipped enemies, perhaps the legionaries might resort to throwing stones or using slings from a distance if they aren't able to get close with their swords.