mug trainer
n.— «From the stable of newcomers Russell and Robyn Rogers who own the Rodmor Stud in Waikato and call themselves “mug trainers,” Veloz did not race at 2 or 3.» —“Racing: NSW hoop scores at Ellerslie” New Zealand Herald (Auckland) Sept. 30, 2007. (source: Double-Tongued Dictionary)
Further reading
The expression to turn on a dime means “to change quickly.” Early on the phrase referred to horses or horse-drawn vehicles and later to motorized ones, and suggested the idea of changing direction quickly and easily without needing a large turning...
The expression to go chalk has to do with rankings in an athletic tournament and harks back to when seeded teams or players were listed on a chalkboard. To pick chalk means to choose one’s favorite competitor, and you can also speak of a chalk...