If my Spearman is in range of a Banner, but the model he is supporting (and all of the other models in the same fight) are not, can I get a banner reroll in that fight? Does it have to be the Spearman's die which gets rerolled, or can it be any allied model, as long as the Spearman is in range of the Banner?

I don't have the book with me so I can't give a reference, however, if my memory serves correctly, the banner reroll can go to any friendly model in the fight as long as one model from the fight is in range. So, if the spearman is in range, it should let any one of the dice thrown for your side in the fight get rerolled.

_________________
"Draw your sword with a heavy heart, but swing it with a heavy hand"