Complex sentence: During that same summer, he had a training stint with Derby County and was offered a contract that could only be put into effect once he received his work permit so Adjei returned to the United States to attend college.
Split into simpler sentences: During that same summer, he had a training stint with Derby County and was offered a contract that could only be put into effect once he received his work permit. After failure to attain his work permit, Adjei returned to the United States to attend college.