It’s rare in professional sport that a coach gets to leave on their terms. Most never get the chance. They are pushed, or they cling to a season too long.  Leo Cullen has given himself, and Leinster, the rarer option: a departure chosen in advance, days after lifting another title at Croke Park. After 32 years at the province as a schoolboy, player, captain and coach, he will step away in 2027 to “move on to a new challenge”. That is the good news. The harder news is what it leaves behind. By the time he goes, Cullen will not…