Tonight at 8:30pm, John Duddy, the popular former middleweight from Ireland who was the personification of a blood-and-guts warrior in the boxing ring, takes over MSG’s “Celebrity Countdown” to rank the top hockey fights from the Rangers, Devils and Islanders’ 2011-12 seasons. Countdown Wednesdays are part of MSG’s Summer Block Party programming lineup that features themed nights every day of the week all summer long.