Among those that are still on our books, Williams, Fish, Kwambala, Bennetts, Fredricson, Ogunneye, Murray and Kamason have all spent extensive times on the sideline (most of them spent more than half of their times since U18s days out injured).
Before them we had Tuanzebe, TFM, (Ro-Shaun) Williams, Laird, Mengi, Pye who have spent at least couple of seasons on the sideline when they were still on our book. The 2 Spaniard FBs were relatively injury-clean though.
You have to wonder what would have been if they were/are more fit. It's already very hard to breakthrough as a defender in your teenager years.
We have injury-prone players in other positions too (Meijia, Ennis, Mather, Moorhouse springs to mind) but the situation of the defenders is absolutely ridiculous.