[ETA: Now ready for download over at MTS!]
The first mod/career mod that I've ever made will be out at MTS, hopefully soon, I submitted it late last night and will update this post when it's ready for download. Some info about it, which will also be reiterated (mostly) on the release via MTS:

Install this mod and add a new Military Career for your Sims with three different career paths: Sims Army, Sims Navy, and Sims Air Force. Definitely worth noting, this new career mod is perfect if you want your sims to become a high-ranking general in the game. Just the base game is needed to use this in The Sims 4 game. By searching sims 4 boxing career mod on Ecityworks, not only can you save time on job seeking but also can find the most satisfactory job. Once you are on Ecityworks.com, never stop at only searching sims 4 boxing career mod, please look for any job you want, for both you and your friends and anyone. Sims 4 Boxing mod Hi, does anyone know where I could find a mod for the Sims 4 which adds boxing, either as a hobby or career? I've been looking for a little while and can't seem to find anything. Unzip the downloaded file and place all those files into your Sims 4 Tray folder, which can be found at Documents » Electronic Arts » The Sims 4 » Tray. Don't forget to download all the custom content listed. Otherwise, your sim won't look like mine. Place custom content files into the Mods folder located at. Read More.

BOXER CAREER
Boxers work hours in the gym to improve at their craft because it's a tough and demanding way to make a living and establish a career.
It could be the toughest of all sports to survive.
Many fighters are drawn to the sport because they love the one-on-one competition and may have seen their heroes emerge victorious in a big fight and they want to emulate that success.
Having that desire is a small part of being successful. You need to have athletic ability and the determination to turn that into fighting skill.
It takes hours in the gym and years to develop the specific characteristics needed to be a great boxer. Do you have what it takes?

Rabbithole: Stadium
Levels: 10
Ages: YA,A,E
Skill Building: Athletic, Logic, Charisma

The Sims 4 Boxing Bundle Mod

Uniforms: I used the following game career outfits for males and females (not including elders) - sweats, athletic, athletic jacket. I'm not sure how to incorporate custom uniforms or I would have tried to put in the boxing outfit, so if or until I figure it out those will have to do. Alternately, you can change the career outfit via CAS or style booth once your sim has joined the career.
Opportunities*: 5 included
Career Events/Chance Cards*: 5 included
Autographs:

Sims 4 Boxers Mod

Ability to hold autograph sessions at the Stadium will be enabled once level 5 has been reached. The interaction will be available by clicking on the stadium.
Possible Future Revisions

• Give celebrity points as rewards for opportunities, events/chance cards, and/or promotions. Need to see how/if this can be done.
• Add more opportunities and/or events/chance cards.
• Find out how to use boxing outfit as the uniform instead of the athletic outfits currently being used for the mod.

[Drayeth Ash and his brother-in-law warming up. Made the Ash legacy just to test this mod, LOL, and they've become a large family of boxers. Maybe one day I'll introduce them, but for now they're my testers.]

S3PE
Twallan's Careers Mod and various tools
Creon for the Complete Guide to Career Modding for Beginners! Tutorial via Sims Wiki

Sims 4 Boxing Career Mod

Staged images:
Fight Poses by Simprov Poses

Sims 4 Mod Boxing Career

So one afternoon about three weeks ago, a sim of mine that had grown up to a young-adult wanted to swipe some of his parent's neat household items when he moved out. He asked me if it was possible to move them from one house to another. 'No!' I replied, 'It simply can't be done!' But he had an interesting idea, 'What if you made a box that was big enough to hold a piano, but small enough I could fit in my pocket?'
'Ridiculous!' I said. 'Impossible!' I snorted.
He just grinned, 'You made lockable doors, most people said that was impossible....'
That sounded like a challenge to me... and I love a good challenge.
After three weeks of work, many failed attempts and dead-ends, and a serious quantity of coffee, I'm ready to unveil Packing Crates for The Sims 4.
This mod adds a 'Pack in Crate' menu item to every item in the game (with a few exceptions) that cannot be normally placed in an inventory. Selecting this menu choice will search the lot for a free packing crate and move that item into the crate's inventory. If no packing crate can be located on the lot, the action will be cancelled.
Crates can be purchased from Storage/Miscellaneous in build-buy for 150 simoleons. The crate was cloned from the crate end-table in the game and will also still serve as an end-table if you want.
After packing objects into a crate, the crate itself can be placed into a sim's inventory and carried with them to a new home. Crates can also be left around the lot for use as storage (or end-tables).
To unpack a crate, place it into the world and open it's inventory. Clicking on an item in the crate inventory will result in a 'Place in World' menu choice. The object will be placed near the crate (it will always appear on the first floor). If the game cannot find a place for the object (for instance, paintings and other wall-art will not place automatically) then the object will be placed into the household inventory. Notifications will appear if there are any problems.
The menu choices and the ability to store objects in the crates are added dynamically by the script portion of the mod, so this is compatible with custom content objects, and all expansion packs (even new unreleased ones).
Warning! - It should be noted that if you remove the mod, any items that are stored in crates will disappear along with the crates themselves! You may want to make sure you unpack all crates on all lots prior to removing the mod.
*MINOR* Bug Notice
There is one bug that I have been unable to figure out, but it's not a game changer. The code has been written to take great care with your objects and not lose them in a move.
When a crate is placed in the sim's inventory, and then the sim moves to another lot or the game is saved/reloaded with that crate in their inventory, when opening the crate it will show all the objects in it as being a stack of two. This is an interface glitch only, there is only one copy of the object in the crate and it will unpack normally. However, after unpacking one copy of the object will appear to still be in the crate's inventory. It's not really there! If you click on the crate version of the object, the menu will appear as if you clicked the actual object, which is confusing but I can live with it. The remaining ghost object will go away the next time the game is saved and reloaded.
Ghost items that have not yet been unpacked will also straighten themselves out if the crate is placed back on the lot and the game saved/reloaded.
Weird... but it doesn't really hurt anything. I'm not sure if the problem is fixable without changing the game's user interface code which is not very accessible.
-Scumbumbo