Complex sentence: Four of the five balks came at junctures when the Cubs' Billy Williams was on base; once in the first inning, and three times in the third inning, when Shaw walked Williams, then balked him to second, third and home.
Split into simpler sentences: Four of the five balks came when the Cubs' Billy Williams was on base: one in the first inning, then three more in the third inning. In the latter frame, Shaw walked Williams, and then proceeded to balk him to second, third and home.