Holzer was selected by the Toronto Maple Leafs in the fourth round (No. 111) in the 2006 NHL Draft, but he remained in his native Germany for four years before heading to North America in 2010 to pursue his NHL dreams.
At 6-foot-3 and 215 pounds, Holzer is a strong, physical, steady defenseman who keeps it simple when it comes to moving the puck. He made his NHL debut with the Maple Leafs on Nov. 6, 2010, playing 12:46 of ice time during a 3-2 shootout loss to the Buffalo Sabres. Holzer played one more game for Toronto that season, three days later, but would not appear in another League game until 2012-13.