Yes, you can cast Shield
Time Stop says:
This spell ends if one of the actions you use during this period, or any effects that you create during this period, affects a creature other than you or an object being worn or carried by someone other than you.
As soon as the caster Attacks or creates some effect that affects a creature other than itself, the spell ends. Once the spell has ended, you can act normally, allowing you to cast Shield with your reaction, turning a potential hit into a miss.