TMZ obtained photos of the country music star with a huge knife in a sheath hanging from his hip. A witness tells us Jimmie showed up Saturday to a Pop Warner game in Lewes, DE to watch a family member play.

Folks who were there say Jimmie had a friendly conversation with the man he was standing next to on the field ... and we're told Jimmie seemed to be rooting for the winning team.

While it's unclear exactly why he had the knife, a source close to the singer tells us he fishes almost daily and is always outdoors, so it's possible he just happened to have the knife on him.

Jimmie's been going through a lot lately ... as we've reported, he's countersuing a woman who is accusing him of sexually assaulting her and secretly filming the alleged encounter.

What's more, Jimmie is also countersuing his former manager, who is accusing him of sexual abuse.

Meanwhile, Jimmie and his wife Alexis are back together after briefly separating when he confessed to cheating on her ... and last month they welcomed their third child together.