Init (1d20+3=10)
Slow to react, Roscoe prepares his light sword to attack. He waits for the spider to come before attacking recklesly.
Reckless attack (1d20+4, 1d20+4, 1d6+3=[15, 4], [6, 4], [6, 3]) - Hit 19, Damage 9.
I think that in 5e there is no problem with attacking and moving diagonally