MLS to implement concussion substitutions; Jeff Agoos explains how 'medical sideline reviews' will work | CBS Sports Headlines MLS to implement concussion substitutions; Jeff Agoos explains how 'medical sideline reviews' will work The new rule allows teams to make two additional concussion substitutes in all American professional leagues, including MLS … Continue reading MLS to implement concussion substitutions; Jeff Agoos explains how 'medical sideline reviews' will work