[4]– Billy Breen on the Ottawa Hockey Club after the first Stanley Cup challenge game on December 30, 1903.

In December 1909, at the onset of the 1909–10 season, the Winnipeg Shamrocks made preparations to enter a Stanley Cup challenge against the Ottawa Senators of the short-lived CHA, and were to bring out Billy Breen, Billy Keane and Harry Kennedy from retirement for the challenge, but the meeting between the two clubs never materialized.

Breen although a light player, weighing in at only 140 pounds, was nonetheless very well built to withstand the game of the early 1900s.

Ottawa Citizen, in their write-up to the December 1903–January 1904 Stanley Cup challenge series between the Ottawa Hockey Club and the Winnipeg Rowing Club, described Breen as a "dashing little center forward" and claimed him to be "one of the most spectacular little forwards that ever hit the ice.

"[10] Breen objected to the over-the-top violence that often occurred in early amateur and professional ice hockey.

[11] Joe Hall, Breen's former teammate on the Winnipeg Rowing Club, was the chief offender on the Maple Leafs during the December 19, 1907 game, rendering Charlie Tobin a deep wound in his temple, and Winnipeg Maple Leafs manager Jack Lee said after the game that he regretted the incidents probably more than anyone else.

= MHA Intermediate *Playing stats from SIHR (Society for International Hockey Research)