His name is written 松坂 大輔, according to wikipedia (I can't vouch for that), and they give the IPA as [da̟i̞s-ke̞ ma̟t͡süza̟ka̟], noting that it is "often rendered as "DICE-k" or "DICE-keh"; he's nicknamed "The Monster" (怪物 kaibutsu)". This may look striking to English speakers who don't know Japanese: we have a word spelled in English with a vowel that doesn't get pronounced: Why transliterate his first name as Daisuke but pronounce it without that second vowel? Japanese has "voiceless vowels", as those who've had an intro to linguistics know. Between voiceless consonants like [s] and [k], high vowels (i, u) sound like an [h] or almost like silence, because the vocal folds don't vibrate during the vowel. The IPA given for Matsuzaka's other name shows a hyphen there, which is not an IPA symbol, presumably suggesting silence. Seems a little imprecise given the level of detail in the rest of the transcription.
But the rule is really much slipperier than the textbook account of it, being highly variable and applying sometimes to mid vowels, etc. Like most sources, the Handbook of the IPA calls devoicing a tendency and says (p. 118 in the current edition) that:
As often as not, preceding fricatives replace them altogether.So, after an s sound, we often get complete loss of the vowel. (If you want to hear the samples discussed in the Handbook, you can download the full set here.) Tim Vance's oldie but goodie (hey, it's from 1987) Introduction to Japanese Phonology devotes a chapter to this phenomenon, with lots of focus on the variability of the process. (There's a big technical lit, some recent on the topic too, but I'm figuring this post is for non-linguists.)
This isn't the first time American English has integrated a Japanese word into our pronunciation while losing a vowel or two along the way. Our word skosh comes from Japanese sukoshi ‘a little bit’. (The meaning has changed for many speakers to be something like 'slightly', so that you hear 'a skosh bit'.) So, how come we lose that last vowel too, instead of saying skoshie? As Vance notes (p. 48), a high vowel after a voiceless consonant and before a pause tends to devoice.
But Daisuke's (nick)name just doesn't sit that well with me: It calls to mind that otherwise forgotten wretch Andrew Dice-Clay. I think I'd call Daisuke "the Monster" or kaibutsu.
Graphic from here.