Well, actually, the most common interaction with police for citizens is traffic-related.
But the bigger grey area is where you mention "theft". Property owners can call the police because of suspicious activity, which is ill-defined. Those altercations can turn bad quickly, with assumptions made on both sides. Most police interactions are non-violent, but 1.4% of them involve police using force or threats. That number is far too high. (This is from the Bureau of Justice Statistics in 2008 report. I can't find a more recent one - there was something published in 2011, but it's hard to parse)