It's rare that a defenseman wins the Calder Trophy. Voters usually go strictly by points, and defensemen rarely score enough to grab votes. That said, the recent injury of Chicago Blackhawk rookie Jonathan Toews is good news for Tobias Enstrom's chances. Toews will be out 3-4 weeks with a knee sprain. He has 32 points in 36 games so far.
There's essentially a four-man race this year, unless a goalie gets hot. Patrick Kane, also with Chicago, leads rookies with 37 points in 38 games, but some say he's not been as good lately, perhaps hitting a wall. Enstrom has 24 points in 41 games, is +4 and is averaging 24:03 in ice time.
After somewhat of a slow start, the Capitals' Nicklas Backstrom is coming on strong too, winning Rookie of the Month for December. He has 29 points in 40 games.
Here' a link to the full stats of rookies.