Yesterday I caught up with a much stronger rider who was struggling with an injury but really wanted to finish. Moral support aside, we tried to get him on my wheel on the flats (which happened to often have a headwind, so even at 20-25 km/h it was well worth it). Up and down hill it seemed better to go independently. But we met up with some other friends so there were 4 of us in total. This gives a few more options.
The rider in question was tough and I'm sure could have done it without help, but in another club/context I could find myself trying to look after a rider who was in real need of an easy ride back. In case it makes a difference, let's assume from yesterday that we're happy (and practiced) with riding pretty close together, but not race-peloton close
How can we best position ourselves (in a small group) to shield the injured rider?