Inside the Park Home Run

This is a very easy fight as boss is pure melee with Pelagos

Boss abilities
Power swing. He will do a front cone swing that deals large damage and does a knock back so don't stand near edge. This can easily be sidestepped to avoid it.
Massive Charge. He will do a charge in your direction. This can easily be dodged. Also point him in a direction that does not make him go clean across the map.
Shielded Charging. He will take a knee and begin recharging power. During this he will put out a shield that rotates around him. GO to the side without a shield to dps

On wisdom is adds Quaking Shockwave which is an AOE around the boss. It will first do a small inner circle and then a larger outer circle around the boss. This can easily be avoided by being at a range. It will toss you in the air if you get hit..

Fight strategy.
Choose pelagos and for equipment choose either vial of serenity (for wisdom because of achievement in case you take a hit) or vial of lich frost. Since he is a pure melee it is very easy to avoid him with aspirant's binding and vial of lich frost. Take the shield from confront memories and dps the boss when it is safe to do so. Make sure to aim him so that his power swing hits you from one set of stairs to the other as this will guarantee that you land inside the arena.. Once he is at low energy he will begin to recharge. Just dps him till he is recharged by going to the side with no shield..

For Wisdom with Pelagos and Inside the Park homerun
His new ability is Quaking Shockwave with is an AOE around the boss which does a smaller inner circle first and then a larger outer circle. Getting his will launch you up in he air.
For the Achievement you will need to get hit by Power Swing 5 times. I recommend doing it aiming from one set of stairs with you back to the other set of stairs as the knockback is really big.
https://www.youtube.com/watch?v=8FhH8Nig7VM

I got this on a Trial of Loyalty version of Athanos, so it doesn't appear to be limited to the Trial of Wisdom as mentioned in the tooltip.

As of 9.1.5, this can still be done on Courage.