When your walking or driving and bump one and he flies away keep a close eye on him often times they'll just go down the road or just up into some cover and land giving you a second chance. Also when you do spot a grouse often times there are others with it that you cant see. So if one flies away the others may not so keep that in mind too.
Had that exact experience yesterday. Saw one through the small brush on the side of a road as I was walking. Tried to maneuver to get a shot on it and it took off in to the trees. It didn’t go far so I walked in to try to find it to no avail. Once I got on the road to keep going, thinking that was it for that spot, I walked about 50 feet and off flushed another. I’m new to strictly grouse hunting and am learning a lot the hard way