Note 201 — Chapter XXXI · HOW A HUNTER SHOULD QUEST IN CLEAR SPIRES AND HIGH WOOD198
Reading edition
The explanation of this sentence is that a stag which entre-marched or sur-marched, or in other words placed the hind foot on the track or beyond the track made by the front foot, was a thin or light deer, and therefore not a fat stag, which latter was what the hunter would be looking for.