I'm thinking of cases like Jesse Williams, where a mob forcibly removed the victim from where he was being held inside the court.
From what I gather in the case of Williams the police looked on and didn't attempt to interfere, was this the norm? Did officers that didn't try to enforce rule of law ever face any possible repercussions? Are there any cases of police engaging in the use of force to protect a potential lynching victim from a mob?
Not a scholarly source, but here's a relatively thorough look at a lynching that meets the parameters you describe in Virginia in the 1920s and prompted a law to deal with such situations. The accused was taken from the jail by force. According to newspaper accounts, deputies were threatened by a larger group of armed citizens and stood aside, allowing the victim to be hauled out of the jail. Afterward, officials promised a grand jury investigation and the governor came to town and lectured the townspeople for resorting to mob violence. But no one was charged, and the town's newspaper remained fairly defiant about the issue. Later, the incident would prompt a statewide anti-lynching law, which dealt specifically with prosecuting officials who let these things happen:
The law, enacted in March 1928, enabled the Virginia attorney general to prosecute lynching participants as well as local authorities. It was never used against whites for lynching a black, but it was the first such law in the country.
edited for formatting and to clarify a point