Correct spelling, explanation: competing is not only an adjective but also a present participle of the infinitive to compete, which was borrowed from Middle French competer and Latin competere. As you can see, the derivative comes from the verb, not the noun competition. That is the reason why it should be spelled as competing, not competiting.

Definition of competing:
1. verb (present participle), to be in a state of rivalry
Mike is always competing with his brother for their parents’ attention.
I don’t think I will win this time. I’m competing with a very strong person.
2. adjective, being in a state of competition
There were two competing versions of what happened that night.
Coca-Cola and Pepsi are known for being competing brands.

Collocations with competing::
Some most commonly used collocations include: competing with each other, competing to win, competing in something, and competing for something.

Incorrect spelling, explanation: competiting is a non-existent word, but we can guess where it came from. This mistake may occur because of the wrong assumption that one should form an adjective from the noun competition. It’s actually not true – the right form, competing, derives from the verb compete.

Incorrect spelling

Incorrect spelling

Incorrect spelling