RAW:
1. Spellcasting suffers a dice pool penalty if the target has cover.
2. Clothing isn't cover.

Question:
Is a Ballistic Shield (or other shields both in the gear and improvised) considered cover and able to protect you from Manabolt (if you kept it in front of you when you saw the caster starting to cast). Or would they be considered clothing?

Anything cover it in the rules? If not what are your thoughts?

I thought that the large shields like the police use count as cover that they can carry with them. If it was manabolt I think that it would depend on if it was see through or not. If it was see through then no cover.

RAW: Ballistic shields increase the armor rating and provide no cover. You got that right.

You might rule otherwise, but that opens up the issue of knowing how the shield is worn and which direction is it facing. The abstract basic rule is easier to use.

Yeah, the balistic shield for example is your typical SWAT team shield as well with only a small balistic glass visor to see through. So semi tehcnially it can count as cover if you know for sure that a) the attack wont just punch through, and b) you cant see part of the guy sticking out from the edge of the shield.

It's simply far faster to assume the guy is partially visible (feet perhaps) or what ever and simply count it as aditional armor rather than trying to cover every bloody angle. And even if the guy is intentionally trying to keep himself fully out of view behind an opaque shield, you still do an opposed test to resolve it one way or another.