Yuan Shu was Yuan Shao's brother-in-law. Yuan Shao and Yuan Shu did not like eachother from the start, but Yuan Shu knew better not to betray Yuan Shao.
3rtqweft wrote:I don't think that the main cause of Sun Jian's defeat was to Yuan Shu's failure to supply food. Rather, it was Bao Xin's rash attack to gain personal glory. This meant that it was Hua Xiong, not Sun Jian (as it should have been), who made the surprise attack. This is not to say that Yuan Shu's idiocy did not play a part, but I think that the only difference would be that Sun Jian would be able to hold his position.
As Napoleon said: "An army marches on it's stomach." This is no exception. Without having food, you can not attack. If you are hungry, you have no stamina, without stamina, you can not attack. Battles did not last an hour, but days or weeks.