I have tested multiple times to see if a giga will attack a titan, and it wont. To the people telling you to run under its legs to escape from a giga, ur gonna get a whole lotta crossfire and after you experience like 6k dmg in 3 seconds, you will die and ur body will render out, thus ending the fight with them. If the giga did attack the titan though, the giga would 10 shot it and the titan will die.