You actually have two different issues....The first is the detention.  If you committed a speeding violation, the office had the right to pursue you on the private property to effectuate the stop.  So... this part was not per se illegal by the officer.Your second issue is the reach into your pockets.  The reach is considered a search of your person.  An officer must have either probable cause or consent in order to conduct a search.  If the officer didn't have probable cause or your consent, then anything he found in pockets could be suppressed and thrown out because of an illegal search.