Chad Marshall is a prototypical towering central defender. He has a rare combination of physical tools and skill to dominate match up with most forwards in the league. When he's in form, there isn't a better defender in MLS.
Marshall is the best header of the ball in MLS on defense. He dominates balls sent into the final third, forcing other teams to play on the ground. He cleanly wins headers and can direct them to teammates to retain possession. While most defenders will just attempt to clear a ball, Marshall directs his headers. It's a rare, but very useful skill.
He's a constant threat on set pieces. He's usually mobbed with a double team on every delivery, but still is able to get to get a head to a ball. If Marshall isn't the sole target, he's even more potent. He's adept at beating a marker and driving the ball on goal.
His defensive technique is very clean and he rarely resorts to fouling. His aerial prowess is well known, but he's adept with his feet. He's able block balls played into the defensive third with an excellent timed toe poke. His tackling form is very good. He makes good decisions on when to stay on his feet or go to ground. His positioning is good, rarely forcing him to play catchup, a good thing since his speed is average at best.
There are two weaknesses to Marshall's game and they are both related to his head. His concussion issues are well known. Marshall has suffered several concussions throughout his career. He missed time in 2007, 2010, and 2012 with concussion related issues. It hasn't affected his tenacity at attacking the ball, but he does have a significant history.
The other is his attitude. He's struggled in the past couple years with consistent performances. He hasn't looked as focused or driven. He struggled to stay in shape and was inconsistent throughout the Crew's 2011 rebuilding season and his injury interrupted 2012 season. He rebounded in 2013, coming into camp fit, leading a retooled back line.
Marshall is a 10 year veteran, but still is only 29. He found his greatest form under Sigi Schmid and reuniting may bring out the best in Marshall once again. He can dominate if he's in form. Playing for a rebuilding club wore on him. Going to an MLS Cup contender with a familiar coach may refresh him.