An Altered List

The following list of items has been altered. They all use some form of wordplay originating from the item, with some being very literal and straightforward, while others are obscure and challenging. You need not solve all of the items (but congrats if you do!), the answer is the category of the original items. Good luck!

• ">->o"
• A hose
• A test question
• Art
• The NFL (if everyone wore red helmets)
• Dirt on a hand?
• A political TV show filmed at Charles University
• 0.0697564737
• Two "Sonic the Hedgehog" characters
• .- / -... .- -. -..
• Harry, Hermione, & Ron
• A typical LEGO minifigure head

This is a list of:

stories by Arthur Conan Doyle featuring his detective, Sherlock Holmes.

The clues should be interpreted as follows:

">->o"

Possibly The Adventure of the Crooked Man, since the symbols form the shape of a man lying down. (Alternatively, he may be Creeping instead, since the quotation marks might suggest movement lines...)

A hose

The Adventure of the Empty House - since if we 'empty' the word HOUSE by removing its middle letter, we get HOSE!

A test question

The Adventure of the Missing Three-Quarter (sounds like a question in a mathematics test)

Art

Possibly The Adventure of the Retired Colourman, since a 'colourman' is an art supply dealer.

The NFL (if everyone wore red helmets)

The Red-Headed League (the 'L' in NFL stands for 'League')

Dirt on a hand?

The Adventure of the Engineer's Thumb (which would potentially be covered in grease)
(The OP reveals in comments that their intention was actually The Adventure of the Second Stain, which might sound like the second hand of a clock is dirty...)

A political TV show filmed at Charles University

A Scandal in Bohemia (Charles University is found in the historic region of Bohemia in modern-day Czechia)

0.0697564737

The Sign of the Four - this number is $$sin(4)$$ i.e. the 'sine of 4'.

Two "Sonic the Hedgehog" characters

.- / -... .- -. -..

The Adventure of the Speckled Band - the Morse code decoded spells 'A BAND'.

Harry, Hermione, & Ron

The Adventure of the Three Students (Harry Potter, Hermione Granger and Ron Weasley are all students together at Hogwarts in the books by J.K. Rowling)