Head wobble is what most assume is--
--- a tank slapper & can usually be brought under control by body balance, handeling of the throttle, bit of muscle & such.
A true tank slapper is VIOLENT in that one will SUDDENLY start to loose control of the handlebars so often one is gripping the bars like death, so throttle is opening & closing as bars go from extreme left & right. OFTEN one loose part of the bar, their body wt is throwen to the front & often their feet come off the footrests.
UNKOWEN to them the front wheel/forks are SNAPPING to the extreme left & extreme right in a fast & violent fashion to where one of both STEERING HEAD STOPS will be damaged or toren off.
The front forks will actually SLAM into the fuel tank & start to ding in the tank (so the defination of the saying 'tank slapper') & just about this time one is simply flung off the bike.
The above can come about when one has the f/end become a bit loose or is actually in the air & possibly lands on the pavement a bit to the left or right.
That should be a bit closer to the defination from the normal front end or forks wobbling to a true 'tank slapper'. I have had a lot of them in my yrs of riding & comp., & only recovered from one, how I do not know.