 Why can't the square-built man defend Trella against the men attacking her?
Trella feared she was in for trouble even before Motwick's head dropped forward on his arms in a drunken stupor. A woman could not possibly make her way through these streets alone to the better section of town, especially one clad in a silvery evening dress. Perhaps she could call one of Motwick's friends; she had no one on Ganymede she could call a real friend herself. Trella swung with her whole body, and slapped him so hard he nearly fell from his chair. Her protector was obviously unwilling, but the dark man, faced with his massiveness, took no chances. The dark man moved in on Trella again as Kregg overtook his quarry and swung a huge fist like a sledgehammer. Exactly what happened, Trella wasn't sure. She had the impression that Kregg's fist connected squarely with the short man's chin before he dodged to one side in a movement so fast it was a blur. But that couldn't have been, because the short man wasn't moved by that blow that would have felled a steer, and Kregg roared in pain, grabbing his injured fist. It smashed on Kregg's head, splashing the floor with liquor, and Kregg sank stunned to his knees. The dark man, who had grabbed Trella's arm, released her and ran for the door. Trella ran to the unconscious Motwick's side. The gravity of Ganymede was hardly more than that of Earth's moon, but the way the man picked up the limp Motwick with one hand and tossed him over a shoulder was startling: as though he lifted a feather pillow. He followed Trella out the door of the Golden Satellite and fell in step beside her. I was born and brought up there, and I was finally able to build a small rocket with a powerful enough drive to clear the planet.” “If Dr. Mansard succeeded in landing on Jupiter, why didn't anyone ever hear from him again?” she demanded. It was peculiarly inappropriate, but not unbelievable, that the strongest and most agile man on Ganymede should be a coward. Trella could get a cab from here, but the Stellar Hotel wasn't far. Trella had the desk clerk call a cab to deliver the unconscious Motwick to his home. For some reason she decided against telling him that the assignment on which she had come to the Jupiter system was to gather his own father's notebooks and take them back to Earth. Motwick was an irresponsible playboy whom Trella had known briefly on Earth, and Trella was glad to dispense with his company for the remaining three weeks before the spaceship blasted off.
 His programming does not allow it
 His programming does not allow it  He is a strict pacifist  He is full of cowardice  He is secretly collaborating with Trella's attackers