Social media site network TruMedia Networks has bought several sports community sites from Boxcar Media, which will remain an independent. Terms of the deal were not disclosed. The sites Boston-based Boxcar is selling off include Red Sox fan blog Sawxheads.com, the Celtics-devoted Celtsheads.com, New England Patriots dedicated Patsheads.com and Blackandgoldheads.com, which caters to Bruins’ fans. Boxcar still has several other sites in its stable, including motorsports marketplace RacingJunk and an ad agency site Agency BCM. Release