Continuity mistake: When Krell jumps out of the tower window, his blue lightsaber is in his right hand, but when he lands, his sabers have swapped hands, with the green one in his right instead. (00:12:21)
Continuity mistake: Tup attracts Krell's attention by firing two shots at him, but Krell is then seen deflecting three blaster bolts. (00:15:41)
Continuity mistake: When Rex releases Fives and Jesse from the brig, Fives' kama is missing as he stands up. (00:11:00)
Continuity mistake: When Rex begins to question Krell in the brig, Fives' kama is missing. (00:16:55)
Answer: I guess that 1) the King assumed that Ventress' droids were meant to capture the Jedi, not kill him outright. When she yells at OOM-224 to shoot Yoda, she evidently failed that expectation. 2) Sending out a bunch of Droidekas after it is plain that Master Yoda has clearly won is not a sign of good sportsmanship, either.