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Does activating a knight next to a robber force the chase robber action immediately?Correct.
I say no due to no actions the same turn after being activated. Furthermore, I'm not required to chase the robber away the next turn correct? Perhaps I'd prefer to contribute to the defense of Catan against barbarians.
Thanks in advance.
As the rules say, chasing away the robber is one of the three actions that a knight may perform on your turn, but only active knights can perform actions, and "A knight may not be activated and then perform an action on the same turn.", so in fact a knight cannot chase the robber away as part of being activated. And of course, performing an action (including chasing away the robber) makes the knight inactive again.
However, the rules do go on to say "A knight can, however, perform an action and then be activated again later in the same turn (though he could not then perform a second action).", so you can chase the robber away and then re-activate the knight afterwards to still be able to contribute to the defense of Catan.