In most cases, ” scratchy playing” is caused by too tight a grip on the tipper. Ease up on the death grip to the point where the tipper has a fair bit of free movement just short of launching across the room. To further reduce any lasting scratchy play, try practicing by repeating 4 reps each of down strokes followed by up strokes.
Loose grip and basic tipper practice will eliminate that annoying scratchy playing.
To prevent the drum from trying to escape, adopt a posture where your knee (of the leg the Bodhran is resting on) is slightly higher than your hip. You can achieve this by lifting you foot onto your toes and resting your heel against the leg of the chair or by using a small inconspicuous block of wood. This will allow gravity to work for you and will keep the Bodhran rolling back into you instead of down your leg and across the floor.