Complex sentence: Kirino once tried to chase Kyosuke and he ran away to play with his friends, but fell down and cried in disappointment, which spurred her to start working hard on her academics and sports.
Split into simpler sentences: Kirino once tried to chase after Kyosuke (who ran away to play with his friends) but she tripped and cried in disappointment. This spurred her to start working hard on her academics and sports.