Eager born January 22, 1984 in Ottawa, Ontario. He attended Immaculata High School in Ottawa. He was drafted in the 1st round, 22nd overall by the Phoenix Coyotes in the 2002 NHL Entry Draft. He was later traded by the Coyotes along with Sean Burke and Branko Radivojević to the Philadelphia Flyers for centre Mike Comrie.
The 2006–07 NHL season would see Eager lead the league in penalty minutes, even though he only played 63 games. That same season, he also won the Pelle Lindbergh Memorial as the Flyer who has most improved from the previous season, as voted by his teammates.
Eager was traded to the Chicago Blackhawks on December 18, 2007 for Jim Vandermeer.
Eager scored his first Stanley Cup playoff goal in Game Two of Chicago vs Vancouver on May 2, 2009 in Vancouver. This led to the Blackhawk's first victory against the Canucks and evened the series 1-1. Eager scored his second Stanley Cup playoff goal on May 31, 2010 in Game Two of the Stanley Cup Finals against Philadelphia. His goal ended up being the game winner, as the Hawks won 2-1. On June 9, 2010, he and the Blackhawks won the Stanley Cup, defeating the Flyers 4-3 in overtime in Game Six.
On June 23, 2010, Eager was traded to the Atlanta Thrashers along with Dustin Byfuglien, Brent Sopel, and Akim Aliu, for the 24th overall pick, the 54th overall pick in the 2010 NHL Entry Draft, Marty Reasoner, Joey Crabb and Jeremy Morin. During the 2010–11 season Eager delivered a "sucker punch" to the Maple Leafs' forward Colby Armstrong. Eager received a five minute major, a match penalty for intent to injure, and was ejected from the game. The NHL further suspended him for four games due to the incident. Midway through the season, he was traded to the San Jose Sharks for a fifth round pick in the 2011 NHL Entry Draft.
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