Entry from British & World English dictionary
1920s: perhaps from bob2, bobby calf being one of a number of collocations where bobby has the sense 'small, short'. Compare with the dialect term staggering bob for a very young calf or its meat, recorded from the late 18th century, perhaps from the pet form of Robert.
More definitions of bobby calfDefinition of bobby calf in:
- The British & World English dictionary