Why aren't there 38 matches if the kata name is La Liga? :D

Please spare us the input validation. Short inputs are fine, but null or invalid inputs just distract. Do one thing, and do it well. Input validation has been done.

"return -1" does not sound very idiomatic for Java. Maybe something else would be more expressive, for example OptionalInt or the Integer and null?

Thanks for the feedback, I have just change it

Note: the array of matches may be incomplete (less than 10 matches played) or empty/null. In this case return -1

You didn't mention that more than 10 also should also return -1.