umped is ump's Past Tense

ump

US [ʌmp]
UK 
Plural Form:umps  Present Participle:umping  Past Tense:umped  
n.
1.
裁判员
v.
1.
当裁判,当裁判
abbr.
1.
【化】(=uridine monophosphate)一磷酸尿苷,尿苷酸