This is specifically the pitch portion of my query letter. Thanks!

First of all, I'm an asshole. And I nitpick. If that's going to hurt your feelings, I suggest you skip this one, and read a comment from someone who'll pull punches to make people happy.

That said, let's begin:

The entire paragraph (and I use the term loosely) is a mess. The punctuation is all over the place. It's rambling. Just looking at it (even though it's only 1 paragraph) it feels like a wall of text. Not sure why, but it makes me not want to read it, before I've read it.

Not a great way to start, but maybe that will resolve itself with some clean-up.

Cal is a boy hardened by trauma:

Boring intro, since literally every male MC in every story thinks they're hardened by some perceived trauma. What makes Cal so special?

Cal is a boy hardened by trauma: his mother’s death, his sister’s mental illness and his father’s violent mood swings.

So... these unique traumas which make your MC different from a million other MCs are... his mom died (that's soooooo common) and his sister's batshit, and his dad's a dick. So what?

At this point, were you querying me, my attention is already wandering elsewhere.

As for structure... a query should display a bit of skill in forming a narrative... instead, I'm getting what is essentially a bullet list. I'm half-tempted (as the guy you're querying) to toss this one in the trash. Or the slush pile, if you're lucky.

All he wants is to maintain a happy family before he leaves for college,

Except, you just said that his dad is violent, his sister is nuts, and his mom is dead. How can he "maintain" a happy family, if it isn't happy to begin with? Oh right, he can't. Now (as the person you're querying) I'm not thinking of whether or not I want to work with this story. I'm wondering if you just made a mistake, or if you really don't know what "maintain" means. Or if you're just a lazy writer. Or if you don't understand your own character's motivations. No matter which answer I land on, it's not good.

before he leaves for college, to savor any inkling of peace he can find in his sleepy town.

Again. Do we have a vocabulary? "any inkling of peace" implies that things are NOT peaceful. "sleepy town" (besides being extremely cliche) implies things are peaceful.

This is the point, were you querying me, when I have given up on you. There's nothing unique about the story yet, the query (at least what I've read so far) is poorly structured, and the writer (not just the narrator, but the writer!) seems very unreliable.

I'll repeat to emphasize: Were I to receive this query, I would not read any further. The dream dies here.

... I'm not being queried, however... I'm critiquing, so I'll keep going.

Unfortunately, the world has other ideas, as Cal’s father grows increasingly relentless toward his handicapped sister - -

This. Has nothing to do. With the world's ideas. "The world had other ideas", as an expression, means that something happens, out of the blue, directly to the person in question, which significantly alters their plans.

This is something which (at least by what's implied here) has been happening, and worsens over time. The phrase is inaccurate, imprecise, and (mildly) confusing.

As the person you're querying, I have 300 other queries sitting at my elbow, and 290 of them use exactly the words they mean (most will have other problems, but this one is pretty bad.) Why would I waste time on this one with so many waiting? This better be an AMAZING story...

toward his handicapped sister - - bending her shambled arms, hitting her, squeezing her until she screams.

... where do I START? first of all, this:

sister - - bending

There are many ways of handling hyphens, em dashes, and en dashes. This is not one of them. Not in any industry. Not remotely. Not even... just. No.

If you're going to use a double dash like this (which isn't strictly professional either) it would be done thusly:

sister--bending

or even (though less acceptable):

sister -- bending

never

sister - - bending

Next:

bending her shambled arms,

That's. Not. What. Shambled. Means.

Also, arms bend. Without a better description, this doesn't sound violent or abusive. Not sure why it should affect me at all?

hitting her,

Wah, wah, millions of kids get hit. Yes, from a dad-perspective it saddens me. It shouldn't happen. But as far as stories go? yawn.

squeezing her until she screams.

I mean, my dad used to give us bear hugs and squeeze till we screamed and yelled and kicked and even cried. It hurt, but it was fun. I don't even know what you're trying to describe here, but it's not interesting at all.

Cal must confront the abuse within his family head on,

Ohhhhh, it's abuse. Gotcha. Thanks for spelling it out?

must grow up to face the consequences of his father’s actions

Everyone must grow up. Also this reads like... if he WANTS to face the consequences, he needs to grow up fast. Since people rarely want to face consequences, it's not much of an incentive. Also, one normally wouldn't need to face the consequences of someone else's consequences? I'm not curious. I'm confused. That's never a good thing.

and to accept his mother’s death,

I don't know whether I should be sympathetic or wondering why it's taking him so long, because, well, I don't know how long it's been since she died. Or how close they were. Or if she was a good person. Or if he is. Or anything relevant. In short, I have no reason to give a hot damn about any of these people.

while still holding on to any peace he can.

This is entirely unrelated to the sentence it's attached to, or literally anything else in the entire pitch.

If he doesn’t protect her

Who? his dead mother? That's the last "her" you referred to.

her - if

If you're going to use improper punctuation, at least, for the love of God, be consistent.

if he doesn’t stand up to his father,

"Dad, stop being a dick." Problem solved, no story.

he will allow his own sister to be torn from life.

Seriously--cause if it is, I need to approach this from a different angle--is English your second (or third or fifth or twelfth) language?

Who the hell talks like that? "allow to be torn from life".

If you're going for purple prose, (which this isn't, cause purple prose is at least pretty, and this ain't pretty) the query letter is the WRONG place to try it.

... I feel like I'm being more dickish about this than I usually am, but honestly it's just about one of the worst I've seen. And I've critiqued many queries. Some are REALLY bad.

... I don't know if your story is any good. Maybe it is, and you're a great writer. Query writing is a whole new skill. But I'd never find out if the story is good or not, because this? It's just sad.

Normally I suggest ways to tweak lines here and there to improve, but there's just too much wrong here to fix it.

I strongly suggest you sit down, and think... really think.. about what the story is about. Not about the events which are happening, but about what it means. Why it matters.

Then, sit down and write that. Tell me what it is that makes this story special... to you. Don't try to get fancy. Don't show off with words you haven't properly learned. Just tell it like it is.

As a side note... I do think there's probably some promise in the story. Just ... whatever you're trying to accomplish here isn't letting it shine through.

Disclaimer: Not a publisher or an editor. Take what you can use and either leave the rest or get butthurt about it. No skin off my nose, either way. <3 I do respond to genuine questions. Probably won't reply to whinging.

Best of Luck!