While attending Starfleet Academy cadets Jean-Luc Picard and Cortin Zweller encountered Chalnoth mercenaries on the planet Yrskatdon while seeking medical attention for their classmate Marta Batanides. (SA comic: "Judgment")
While serving as Captain of the USS Stargazer, Picard was dispatched to the Chalnoth homeword of Chalna (known on Federation star-maps as Kaus Borealis Five) in order negotiate dispute about a Federation reseach colony on the planet Ynathaia, that the Chalnoth claimed as their own. Picard defeated a Chalnoth champion in a trial by combat, through which Picard secured the safety of the colony until their research was done. (TNG comic: "Children of Chaos")Chalnoth article at Memory Alpha, the wiki for canon Star Trek.