Thanks for the helpful comments.
I only thought of Roger Connor after I read this on Google:
By 1860 there were more than 55,000 Irish immigrants living in Connecticut, making it the largest ethnic majority. Most were unskilled and found work in urban areas like at Waterbury's many brassware and clock-making factories. During the latter part of the 19th and early 20th century, many boxing events occurred in Waterbury. This was due in part to the national popularity of Irish boxers like "Gentle Jim" Corbett and John L. Sullivan.
Roger Connor was a six-foot, three-inch left-handed baseball player. Born in Waterbury in 1857, he played first and third base with a series of teams, including the Giants and Phillies. He was inducted into the National Baseball Hall of Fame in 1976, more than 40 years after his death. He is buried at St. Joseph Cemetery in Waterbury.
I also noticed that Roger Connor's ears protruded noticeably, like my mystery guy's ears, and they also share a thick neck. Since the photo was taken in Waterbury, I thought it might be a long shot.
Below is a composite of the mystery man and photos of Roger Connor:
