There was always a chance of injury when sparring. Particularly when sparring with someone that you were particularly competitive with (like ones brother). Hadyn didn't even remember how it happened, other than a series of complicated moves, and progressively annoyed Jordan. He'd lost his knife, but thanks to Elisha's training over the past year, losing his knife was no longer the most worrisome thing in a match.
He'd blocked a slashing motion from Jordan, and had moved to step in and disarm his brother when Jordan suddenly (and unexpectedly) changed tactics. He let go have his knife and latched on to Hadyn's arm before he was able to adjust and scramble back- and then, between his own twisting, and Jordan's- he felt the searing, hot pain rip through is shoulder as he came crashing down on it, Jordan having flipped him, almost without his notice, onto the training mat.
Surely people would forgive him for looking pained as he gets his shoulder iced and wrapped before heading to the theatre to work.