That doesn’t seem like something that’s out of the realm of possibility if we stretch “language” a bit, but at the same time, a school principal should definitely know guns don’t belong in schools.
Until then, we can only speculate on what Ernie Hudson’s Darryl does that requires Tom Selleck’s Frank Reagan and others to get involved.
That said, maybe things have been escalated to a state where he feels that’s the only way to bring peace back to the school.
Perhaps Hudson’s character threatens a student with a gun?