One of the dumbest (trolling?) posts about rugby league ever made on this site, showing an abject lack of understanding.
You coach individual players to get better at their on-on-one defence, you don't leave it up to them and each other. and if they can't do it, then as head coach you manage your roster over time to ensure that you have players that can individually defend.
And on top of that, as a coach you also work on the collective defensive systems, tactics and scenarios, so that you can instruct your selected team accordingly for any match day - and during the match as situations change.