The Redcap is a Small creature, but it has an ability called Outsize Strength:
While grappling, the redcap is considered to be Medium.
The spell enlarge/reduce, when using the enlarge effect, says:
The target's size doubles in all dimensions, and its weight is multiplied by eight. This growth increases its size by one category-- from Medium to Large, for example.
So while grappling, the Redcap's size is considered to be Medium. Then suppose one of his allies casts enlarge on him. Is his size now considered to be Large? And if so, what happens to his size when he is no longer grappling, but still under the effect of enlarge?