United Airlines does not comply with baggage policy from IATA Resolution 302?

UA Baggage Rules do apply but the reasons offered by the "accepted" answer are incorrect. Res302 doesn't apply to your journey. For journeys beginning or ending in the USA, the USDoT regulations take precedence over IATA Res302.

USDoT requires that the first marketing carrier's baggage policy is applied. In this case, that's segment 1 of the journey, Indianapolis to Newark, marketed by UA. From their website, it looks like UA policy is the default FMC rule. (Some carriers have a MSC policy).

The process to work out which carrier's baggage rules apply to your journey is:

1. determine applicable regulations (USDOT, CTA, RES302)
2. the first marketing carrier decides whose baggage rules to use (based on MSC or FMC)
3. that carrier's baggage rules apply to the whole Journey
4. if there is a stop of greater than 24 hours on the ticket, subsequent segments are charged as a separate Journey

Note: US DoT legal summary

§ 399.87 Baggage allowances and fees. For passengers whose ultimate ticketed _origin_ or destination is a U.S. point, U.S. and foreign carriers must apply the baggage allowances and fees that apply at the beginning of a passenger's itinerary throughout his or her entire itinerary. In the case of code-share flights that form part of an itinerary whose ultimate ticketed origin or destination is a U.S. point, U.S. and foreign carriers must apply the baggage allowances and fees of the marketing carrier throughout the itinerary to the extent that they differ from those of any operating carrier.