Tavern Brawler

Tavern Brawler is a weird striker that relies on improvised weapons for their abilities. They can easily grab one with Chair Grab. It can still only be used once per turn, so if you don't have another weapon be careful you don't break it too early. Here is where Martial Artist has an advantage over a Fighter→Tavern Brawler, they can always use unarmed attacks. Those without unarmed attacks may want to consider having daggers on them as back up, or using a longsword for their weapon.

Bottle Smash and Bottle Toss are both attacks that break the improvised weapon and apply daze. Bottle Toss has longer range, but it also costs a bit of mana. The drawback of breaking the weapon isn't too bad as long as you use it as the last action in your turn. Bottle Smash also has the prone keyword, letting it be used while you're on the floor. This is relevant because of the Tackle ability.

Tackle is a bit of a double-edged sword. It costs no AP, but also deals no damage. Knocking the enemy prone is powerful, but even if you land the attack you will also fall prone. The enemy can also dodge it to make only you fall prone. This is not all bad though. Standing up is only 1 AP, so if you land the knockdown you could spend 3 AP of attacks against the target against which they will struggle to react. If they choose to avoid your attack by spending an RP, you have now wasted one of their RP's for only 1 AP of your own, which is more efficient than a normal heavy attack. You can also use it at the end of your actions, knock yourself and the enemy prone the hit them with the bottle smash.

Improvised Defense's effectiveness relies greatly on what is around you. Something like a table would be very effective cover, but you may not always have that luxury. Tavern brawler requires some level of creativity to get the most use out of.