"Solange der Mensch spielt, ist er frei."
Der Mensch means man, while der Mann means male man. It is the like the difference between homo and vir in Latin. English can sometime be awkward because there is no special word for male man. Often person is substituted, but that can sometimes be problematic as well because person is a more abstract concept.
the verb in sentence can only be in position 2 or at the end. The clause "solange der Mensch spielt" is all in position 1 so "ist" must come next. It feels arbitrary as English speakers, but it is the way it works. http://german.about.com/library/weekly/aa010910a.htm
CONJUNCTION FIRST, VERB LAST http://german.about.com/library/weekly/aa010910a.htm