Rear suspension tends to 'tramp', hop up and down, when large amounts of torque are applied. If you have a more powerful than stock engine, to counteract this, you can fit anti-tramp rods a.k.a. Traction Bars.
The traction bar stops the wind-up of the spring.
The Datsun Competition setup is for a dedicated track car:
The traditional street/track setup is like this:
'Slapper Bar' Street/Dragstrip Setup
This is like the other photos, except the front is not solidly mounted to the chassis. It doesn't interfere with normal suspension unless wind-up occurs. Plus it has a little "play" so that it hits, it slaps, bites down to help traction.
The famous Lakewood traction bar: