Yes you do. "
At least 24 Top 30 players must be contracted by the first Monday in November November and 29 Top 30 players by the first Monday in March and 30 Top 30 players by the first Monday in August."
Here are the official guidelines for the NRL salary cap, including frequently asked questions like what players can earn outside the salary cap, how much can clubs spend, third party agreements and more.
www.nrl.com
"Contracted by", does not mean still under contract, or under contract at that time.
If you stop for a second and think about it, the rules have to allow for all kinds of shit that may or may not happen.
This kind of thing ( mid season transfer ) would be one of those things.
I mean assume for a moment a club wants out of a player, for whatever reason, and the club that then contracts him does so at unders, with the original club making a payout within that salary cap year, not leaving enough room in the cap to replace that player, even at minimum for the remainder of the season.
Unlikely as it may be, there has to be a mechanism for that to be able to happen.