Let me be a little more specific.
A friend of mine was flying a light aircraft into a 2500 ft strip. This is a day VFR strip, with a permanently displaced threshold of 600 ft, due to obstacles on the approach. The dislacing obstacle is a 600 ft hill, ending 2 miles from the runway. It is very easy to turn final inside the hill, and avoid the obstacle all together, and is common practice at this airfield. The aircraft in question requires about 1800 ft to land at gross, and as this runway has 1900 available, it is perfectly 'legal'.
Long story short, the local authority was watching this particular day and witnessed him touching down before the threshold, and wishes to persecute him for it. Every single aircraft that day, and every day for the last 10 years has touched down before the threshold, but they chose him to penalize.
When he asked the authority where the regulation was located, he was informed that 'it is basic aviation knowledge'.
I personally don't feel that it is 'basic aviation knowledge' and wish to find the truth.
I would be perfect happy with either result. If it's illegal, I can give up my search, and admit defeat. If it's legal, he can point out the mistake to the authority.
Thanks in advance for everyone's help.