In Nebraska, a police officer must have reasonable suspicion in order to pull you over. What does this means? Basically, you can't just be pulled over because of a "gut feeling", or for no reason at all. But what are considered valid reasons for a traffic stop, in that case?
As stated by FindLaw, traffic stops usually occur because there has been a small violation of the law. Generally speaking, they'll be "common" violations, or things that would usually result in a ticket rather than an arrest. Examples include aggressive roadway behavior like speeding, running through red lights, or not stopping properly at stop signs. Related to that, one common issue that drivers under the influence have is weaving through lanes or being unable to keep up with the traffic flow. Sometimes they'll be pulled over for these behaviors, and may end up facing DUI charges after.
You can also be pulled over even if you haven't committed any traffic crimes. For example, police can pull you over if one of your headlights or tail lights is broken because it's a potential safety hazard for others. They can also pull you over if the sticker on your plate is expired, as that means your registration has not been updated yet.
If you believe that you were unlawfully pulled over, you may be able to contest any evidence found against you in court for that reason. It might also be in your best interest to consider contacting an attorney for further legal guidance.