Complex sentence: Accelerator was physically weak because of his total reliance on his powers and his overconfidence in his psychic abilities resulted in his defeat as Tōma beat him with his Imagine Breaker and street-fighting skills.
Split into simpler sentences: Accelerator was physically weak because of his total reliance on his powers. Overconfidence in his psychic abilities resulted in his defeat as Tōma beat him with his Imagine Breaker and street-fighting skills.