We are interested in two outcomes of the samme sample space. This is, The first outcome is , and the second outcome is . The answer follows, since every outcome of the sample space is equally likely.
If the first toss is , Martin can never win, since as soon as is seen on any subsequent toss, the game stops, and Gale is awarded the win.
If the first toss is , then if the second toss is also , Martin wins. Otherwise, if the second toss is , Gale wins, since as soon as a subsequent toss shows , Gale is awarded a win.
Thus, Martin loses of the time.