"Introducing the Catchers"... will there be pitchers?! Whoever proposed this name is a troll :)
Firstly catchers is derivative from a verb and doesn't sound good. Also it has some specific associations. Not only baseball. It feels more like "catching a thing" rather then "locking smth down or imprisoning". At least you didn't name them "lockers"... or "graspers"... or "snatchers"... or "fasteners". :)
"Grapplers" would be better but it has strong associatoins with sports. And it's more like Amumu playstyle. "Condemners" maybe?! But I feel it's bad. Also Vayne association.
What about professions? From real life or from fantasy. Like profession names from prisons or medieval themes. "Executioners"?