In this specific context, 'caps' (short for 'caps off') means "finishes", "completes" or in a closer simile: "tops off"
This is basically a metaphor for many different physical constructions - the final piece may be referred to as a "cap stone", which clearly always sits on the top, hence the alternative "tops off" - a thing that provides "the icing on the cake".
In this usage, 'cap' has nothing at all to do with the type of hat that is metaphorically (or sometimes physically) given to a player to signify team membership.