Pendulum swings in an oval shape instead of side to side

by E Post
(Topeka, Kansas, USA)

The pendulum on my Seth Thomas grandfather clock swings in an oval shape instead of side to side.

The oval shape of the swing means that the pendulum swings close to the far left weight and brushes against it.

After a few minutes, the clock stops.

There is a brush mark on the pendulum where the weight touches it.