Sieghart is pretty strong but that’s not going to phase Ryoma. Ryoma has tennis skills at the ready and he can serve up those balls really quickly. I’d like to see Sieghart try to counter his attacks because I just don’t see it working. Ryoma’s skills are almost literally out of this world. He has no weaknesses in his Pinnacle of Perfection mode which is bad news for Sieghart and any hope he had of claiming victory. Ryoma wins.
Update 8 7 2020 Sieghart’s strength would ultimately be enough to stop Ryoma. Sieghart wins.
DReager1.com 
It’s been a dog’s age since I’ve seen Rave Master, but Ryoma has no chance. Given what he goes through, a tennis ball will only be a mild sinus headache to him. Sieghart casts magic, and leaves him be.
Sieghart’s magic definitely does seem dangerous, but Ryoma has been shown to have a ton of destructive power in his serves. A whole boat nearly got destroyed while he was playing