In a game of Scrabble, the original word on the board was “AMEND”:
AMEND
I added an ‘S’ to the end to spell the word “SPA” vertically.
AMENDS
P
A
I thought it was a legal move, but it was contested by one of my opponents. Is this a legal move or not?
Yes, that is a legal play.
As long as your tiles are all in a single row/column and form a single word it's a legal play. This question explains this further.
Your play is a very common technique to get extra points. The linked to answers in the comments are examples of similar plays that get many extra points. As @jolenealaska says, it was a very good play.
