Six in the fourth place means:

The headboard of a young bull.
Great good fortune.

This line and the one following it are the two that tame the forward-pushing lower lines. Before a bull's horns grow out, a headboard is fastened to its forehead, so that later when the horns appear they cannot do harm. A good way to restrain wild force is to forestall it. By so doing one achieves an easy and great success.