Pin oaks tend to not have showy falls colors, so I would not expect much beyond that. It is not normal to have leaves browning at this time of year. Drought or excessively wet conditions can lead to this as can some environmental issues or even some pathogens. If you are seeing some unusual weather conditions in your area and the leaves browning is not extreme, then I would not worry about it. If you are seeing this across the majority of the tree canopy or seeing it during otherwise good growing conditions, then I would seek out a local arborist to assess the tree.
