If you believe you have been unfairly given a fine by the police, your best course of action would be to consult with a qualified attorney who specializes in traffic law or civil rights.
To proceed with a lawsuit, you would typically need to gather evidence to support your claim. This could include any relevant documentation, such as the ticket or citation you received, witness statements, or any video or photographic evidence you may have that supports your version of events. It may also be helpful to document any details about the incident, such as the time, date, location, and weather conditions.
Keep in mind that police officers are generally presumed to be acting within the scope of their duties and have discretion in enforcing traffic laws. However, if you believe you were targeted or treated unfairly due to discrimination, harassment, or other unlawful actions, you may have grounds for a legal claim.
Again, it's crucial to consult with an attorney who can provide specific advice based on your jurisdiction and the circumstances of your case. They will be able to guide you through the process, assess the strength of your case, and provide legal representation if necessary.