Only as a descripted term, such as "the baserunner should not go wide of the bag when rounding the bases", or, "pitcher should go wide (pitch outside) to this hitter".
The term you're most likely asking about is "ducks on the pond," which means runners on base. It's most often used to refer to a situation with the bases loaded.
Fan is short for the word fanatic. A fanatic is someone overly enthusiastic with much devotion for something. At a ballpark you will see the patrons screaming and yelling (enthusiastic) and strongly...