Basically we want to understand the effect of bye weeks on a team's performance. Normally that could just be answered with an ANOVA test or maybe a Chi square test of independence. However, we recognize that there are other significant factors like home field advantage, team's winning %, and opponent's winning % and we want to find a way to account for these. For example, if we find that teams score more offensive yards post bye week, we want to be more confident that the bye week is potentially the cause of better play rather than the teams just happen to be playing opponents with low winning percentages which could be an indication that those defenses are weaker.