If its the other players turn, they choose not to attack, can i still assign defenders?
Attack Phase.
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
If its the other players turn, they choose not to attack, can i still assign defenders?
No. Attack phase is optional. http://rules.l5r.com/CE_Sequence_of_pla ... ptional.29
If there is no Attack Phase, there is no assignment.