Illegal pitch/delay dead ball

[Gleighty]

There were no runners on, so I am assuming it was an illegal pitch. No deception intended. The pitcher's started, stopped, then started delivery. Umpire indicated illegal pitch with a dead ball signal and verbal call. Pitcher deliver the pitch that was hit and batter/runner reached first base. Umpire let the play stand. I felt this was the correct call. Coaches of the defensive team argued that it was dead because of the dead ball signal and the play went against them.