The names of the festivals in Olympia and Delphi are not mentioned by Pausanias, but are very clear from the context:
'τετράκις γὰρ δὴ ἐν ἀνδράσι κατεμαχέσατο ὁ Τίσανδρος πύκτας ἐν Ὀλυμπίᾳ, τοσαῦται δὲ καὶ Πυθοῖ γεγόνασιν αὐτῷ νῖκαι, Κορινθίοις δὲ οὐκ ἦν πω τηνικαῦτα οὐδὲ Ἀργείοις ἐς ἅπαντας ὑπομνήματα τοὺς Νέμεια καὶ Ἴσθμια νικήσαντας.' ('For Tisandros won the boxing match in the category for men four times at Olympia, and there were as many victories for him in Pytho. But the Corinthians nor the Argives kept records at all at this time of all those victorious at the Nemea and the Isthmia.').
It is however not clear whether Tisandros competed at the Isthmia and the Nemea, wherefore Farrington marks him a doubtful Isthmionikes.