Playing soccer in the morning and softball in the afternoon was exhausting, however it was worth it because we won both games.

Playing soccer in the morning and softball in the afternoon was exhausting; however, it was worth it because we won both games.

The first sentence connects two independent clauses with the conjunctive adverb however and only a comma. The second sentence is correct because it adds a semicolon before the conjunctive adverb.

For more help, see section G6.