Can you help resolve a dispute please. On the scrabble board the word "SUM" had already been placed, written horizontally. My scrabble partner added the letter "P" onto the end of "SUM' to make the word "SUMP". In his same move and at the same time, he added the letters "LO" above the "P" that he had just placed, to make the (vertical) word "LOP". Is this a legal or an illegal move ?
Thank you :-)