Why does Mars Bar hide from Maniac Magee when they first start to run together?

In chapter 44, Maniac Magee begins seeing Mars Bar Thompson on his early morning runs but notices that Mars Bar is quick to avoid him.
One reason Mars Bar may avoid Maniac on their early morning runs concerns their controversial past. Earlier in the novel, Mars Bar challenged Maniac to a foot race and lost badly. Mars Bar was embarrassed when Maniac turned around in the middle of the race and beat him running backwards. Mars Bar's pride was sorely bruised that day and fueled his hatred for Maniac. Mars Bar also does not like Maniac because Maniac invited him to the racist McNab home where a fight broke out between the Cobras and Mars Bar after he made a comment about the smell of the McNab residence.
Overall, Mars Bar is not a fan of Maniac and is somewhat ashamed because he previously lost to Maniac in a foot race, which is why he purposely avoids him. However, Mars Bar and Maniac eventually become exercise buddies, overcome their differences, and beginning running together in the mornings.