Look! The strawberry roan is rearing! (6)
I believe the answer is:
Here is my best explanation:
'look' is the definition.
(informal term for a look or glance)
I can't explain the rest of the clue.
(Other definitions for gander that I've seen before include "male member of the Anatidae family", "Butchers - goose", "He has webbed feet", "Ranged over the bird", "town in Newfoundland", "Ranged about with male goose", "Looking at something - ranged (anag)", "Glimpse", "Look - bird" and "Goose sauce is good for it".)