For anyone here familiar with the Powered by the Apocalypse (PBTA) engine: I'm currently having a hard time understanding combat. It seems like in most hacks, any time a PC uses the Seize by Force move or its equivalent, they take at least one Harm; this means that a protracted fight is almost always going to be lethal to them since there doesn't seem to be a way for them to avoid Harm. Am I misunderstanding something?

Can someone explain how a PC could theoretically make it through a successful combat without taking any Harm? Since they have to use Seize by Force at least once, and it seems that move guarantees at least 1 Harm to the PC, is the system set up such that combat always brings at least 1 Harm to the PC? Is that just the way the system is designed?

To seize something by force, exchange harm, but first roll+hard.
On a 10+, choose 3. On a 7–9, choose 2. On a miss, choose 1:
• You inflict terrible harm (+1harm).
• You suffer little harm (-1harm).
• You take definite and undeniable control of it.
• You impress, dismay, or frighten your enemy.

So if one character takes 3 harm from their opponent's weapon and is wearing 2 armor, they'll net 1 harm.  They can always choose the "You suffer little harm" choice and negate that last harm.  On a 7-9 they could choose this twice and on a 10+ three times; negating quite a bit of harm.  Of course, their opponent may have also rolled well and be selecting "You inflict terrible harm"....

Thank you for the answer. A few follow up questions:

1) So you can select the same option more than once? That is a huge element to the rules I missed, and makes all the difference! Thank you for clarifying!

2) You mentioned the opponent rolling well; I thought only PCs ever rolled, and the GM does not? Or were you just referring to a potential PC vs. PC conflict?

I don't find it ever spelled out in the book but has been discussed on forums that some choices are repeatable.  Supposedly one of the game authors has approved examples that include doing so.  I think it's something you'll have to decide for your game.

You're right, only PC vs PC could they counter each other.  In fact the example on p169-170 has this

I think I'm wrong about being able to make the same choice multiple times UNLESS a particular move explicitly says so or you homebrew it.

BUT if the PC does take harm even after selecting "You suffer little harm (-1harm)" choice don't forget the Harm move itself.

When you suffer harm, roll+harm suffered (after armor, if you’re
wearing any). On a 10+, the MC can choose 1:
• You’re out of action: unconscious, trapped, incoherent or panicked.
• It’s worse than it seemed. Take an additional 1-harm.
• Choose 2 from the 7–9 list below.
On a 7–9, the MC can choose 1:
• You lose your footing.
• You lose your grip on whatever you’re holding.
• You lose track of someone or something you’re attending to.
• You miss noticing something important.
On a miss, the MC can nevertheless choose something from the 7–9
list above. If she does, though, it’s instead of some of the harm you’re
suffering, so you take -1harm.

After all that you take your licks and deal with the consequences.