The new rune, shield bash seems like a really cool concept but decently simple. Then I had the idea of this being a high risk, high reward alternative keystone for tanks and bruisers to sacrifice some tank for damage, think of it as a grasp but the sustain part of it was traded out for more damage, yet in a way evens out the trade.
_After gaining a shield, your next basic attack within 0.8 seconds deals bonus adaptive damage equal to 35% (+1% per 7bAD and 12AP) (+1% per 30 bHP) of the original shield amount, consuming that amount of the shield and granting you 20%-38% move speed (based on level) for 1 second. If you do not attack within the 0.8 seconds of gaining a shield, your shield amount is increased by 14%-50% (based on level) but no more than (25% of your maximum health)._
The numbers are far from perfect but as an idea i think it reaches a good balance for tanks or bruisers to alternate from turtle-ing up and adds risk to opting in for more damage. The increase on the shield after the timer is up is there so that you are not holding onto a useless keystone and so that stopping yourself from attacking whilst your shield is up is less of a down side for if you want to prioritize survival. The cap on the shield increase is there for the Tahm kench's of the world that could get frustratingly fat from this keystone and remove themselves from the possibility of death,