i remember Chiba Sensei telling me about an encounter between Tohei and a sumitori who "challenged" either Tohei personally or Aikido generally (It was a long time ago and late at night after a few drinks).
He said that Tohei Sensei defeated him but was very brutal - adding that of course there were no cameras present, his opponent was Japanese and Tohei was really pissed off with him..
Chiba told the same story here:
Q:What about Master Koichi Tohei of the Ki Society?
A:Yes, Tohei Sensei is very good. He is small but very powerful. I saw him take a challenge from a wrestler once.
Q:Sumotori or Western style?
A:Western style. Two brothers - Germans I think from Argentina - and they were enormous! They had to bend over to avoid hitting their heads on the gate-post of the Hombu. This was the only time that O'Sensei accepted a challenge for Hombu. These people were travelling the world with a film crew and were challenging different Martial Arts masters. They had been to the Kodokan (Judo HQ), but the Judo men had not been able to handle them. So they challenged the Aikido Hombu. When they arrived I met them and brought them in. Inside the dojo were O'Sensei Kisshomaru Sensei, and Tohei Sensei who was then the Chief Instructor to the Aikido Foundation. O'Sensei nominated Tohei to go first, as he was so strong. So the wrestler crouched in a low posture with his hands out stretched in front of him, and just moved in a circle around Tohei Sensei for a long time. Tohei Sensei was very relaxed and just followed his movement, and eventually cornered him. Just as the wrestler began to move Tohei leapt upon him, threw him to the floor, and bounced his head for him. Tohei Sensei then pinned him down with his hand blade extension, which, as you may have heard, is very powerful. This guy could not move, and his brother declined to try Tohei for himself, so that was that. Apparently at the Kodokan the Judo men advised them not to make a grab for an Aikido Master. That is why he circled Tohei Sensei for so long.
I suspect Chiba Sensei was talking about the Rendezvous with Adventure guys. This event happened the same year Chiba Sensei started Aikido (he was 18 years old Aikido noob in 1958) and probably misunderstood Hermann's name with German nationality.... assuming he was really there when this happened.