I'd be curious to see your solution in this case. :)

Why are there multiple rows if results from a single player

To have more than a single test?

Why aren't the table and column names given in the question? This is an easy problem so should give all required information up front without needing to read the test cases.

The initial code is giving you all you're asking here:

-- you will be given a table, goals, with columns la_liga_goals, copa_del_rey_goals, and champions_league_goals. Return a table with a column, res.

A conditional block could be used in the kata description, but not everyone knows about them.