Correct spelling


Correct spelling, explanation: hitting comes from the base adjective to hit. When adding the -ing suffix, many nouns ending in consonants such as, for example, t, d, g, b tend to need a doubled letter added before the suffix, mostly because that way the pronunciation is more intuitive to the speaker.

Definition of hitting:
present continuous or adjective of the base word to hit.
1. To punch, smack, strike something, or into something with a hand or an object
The noise outside sounded like a baseball bat hitting a trash can.
He angered me so much that I felt like hitting him in the face!

Incorrect spelling


Incorrect spelling, explanation: hiting immediately makes you think about the pronunciation of hiring because of this spelling. This is why it’s an incorrect form. Hitting has what hiting lacks because of the proper doubling of the letter t, which makes the reading much more intuitive as it better suggests where and how the base word ends.