Fernando Tatis Jr was declared “likely done” for the season after a swing at the plate injured his back. Team officials are calling it a “stress reaction”. Video review shows twisting and extension of his back at the time of the injury.
Although stress reaction isn’t a clinical diagnosis, a likely scenario is that the twisting motion resulted in either an annular tear of one of the lumbar discs, or a lumbar facet joint injury. Either could have caused the lumbar musculature to spasm, making it difficult for Titas to continue playing.
Hopefully, the inciting injury is minor and with some rest, physical therapy and possibly injections, the inflammatory stress reaction would diminish and he could be able to return in a few weeks. Although, with the Padres hope for a playoff spot waning, he might be kept out for the rest of the year as a precaution.