There are lots of options available and many were mentioned. Without repeating too much, I hope.
There is a Wrestling Skill that can be purchased. I think it's in Arms Companion and I believe it is ST/ST/AG, or ST/AG, I have to look that up.
MA Sweeps and Throws includes the "ground fighting styles" (Judo, Aikido, Wrestling) vs. the kicking striking styles (Kenpo Karate, Tae Kwon Do, Muay Thai). Martial Arts doesn't mean "from Asian lands where people eat with chopsticks and have shaved heads", it's a studied style of martial combat, including the wrestling styles; American Indian, Olympic, Greco/Roman etc.
For a simple "bull rush" type tackle, there is the Ram/Butt/Bash/Knockdown table from the core rules.
Brawling attack table is an option, but is very weak and as defined, I believe is "improvised weapons", beer bottle, chair leg, rock from the ground, pouch of gold, etc. so that may not apply for what your PC wants to do.
If the goal of the PC is to just "send the target to the ground", the Unbalancing Crit table, or Krush table (for a fall to the ground).
If the goal is to "take the target to the ground to immobilize" then the Grappling table is excellent. If available, there is also the Stun Crit Table and the Sparring table. The latter items are dependent upon how many additional RM Companions you purchased as there are quite a few.