This is one of the most deceptively difficult core exercise you'll ever attempt. It's basically a single-arm plank while holding the bottom position of a renegade row. As a fresher, here's what the standard renegade row looks like:
Why not just do a standard renegade row to target your core? Well, it's not as effective. First, most renegade rows involve repeatedly lifting and placing the weight back on the floor each rep, minimizing constant tension to the core musculature.
Second, while the core plays a key role to stabilize the spine during renegade rows, the act of rowing the weight upwards and moving into shoulder extension causes the lats and upper back to work just as hard as the core to resist rotation. When the weight is held in the bottom position as shown below, the lats and middle back can't be relied on as heavily to resist rotation, placing a majority of anti-rotation responsibilities on the core.
Renegade Plank Hold
In a regular renegade row, the phase of the lift where the core is most heavily engaged is when the weight is in the bottom position, just above floor height, before the weight is actually rowed to the top.
It's when the weight is in this bottom position that force vectors responsible for resisting rotation on the spine and core are at their peak. It's also where and the lats and upper back contribute very little to anti-rotation but instead act mainly to stabilize the shoulders and keep them from excessively protracting.
That's why you should perform renegade rows in an eccentric isometric fashion using continuous tension by never placing the weight back to the floor until the set is complete. Basically, use your core instead of the ground to support the bottom position.
This variation also allows you to support your weight on the forearm rather than the hand. This places even more tension on the core by reducing the degree of shoulder and triceps involvement.
Finally, the elevated position requires continuous core engagement. It's impossible to collapse or rest the weight on the floor between reps. The degree of intramuscular tension throughout the entire body is difficult to replicate with any other exercise.