デ杯 is read as ではい (dehai) and means Davis Cup.
ではい
dehai
さかずき
sake cup
いっぱい
one (boat)
ちからいっぱい
with all one's strength
ぎんぱい
silver cup
せいいっぱい
the best one can do
はらいっぱい
to one's heart's content
まんぱい
full
くはい
bitter cup
げんきいっぱい
brimming with health (vigor, vigour)
ていっぱい
having one's hands full
めいっぱい
to the limit
かんぱい
drinking one's glass dry