Work out each combat one at a time in the order chosen by the player whose turn it is - resolve each combat completely, including any flee and pursue moves, before moving on to the next combat.
A combat is often a fight between a single unit of troops from each side, but it is possible that several units, monsters and heroes may become involved in the same fight (see Diagram 33.1 - Examples of Combat). So long as fighting units are interconnected, they are participating in the same combat. The combat results for such a combat apply to all the units involved.