Trademark - I want to trademark a word that is included within an existing trademark. Different Classes.

The standard is liklihood of confusion in the relevant market. You appear to have two distinct markets so the remaining question is if AthleteXX is so distinctive or has achieved such notoriety so that even different markets (social media and apparel) make the mark deceptively similar. There is no answer with scientific certainty, it is a subjective call.

I think no - the marks are too similar, and customer confusion is likely. However, reasonable minds may differ.

I think the two are two close so you are very likely to draw a 2(d) refusal [refusal to register based on likelihood of confusion]. Of course, we can't give an informative answer without the real marks, and this is a judgment call for a trademark examiner at the USPTO to answer. To quote TMEP 1207.01 "there is no mechanical test for determining likelihood of confusion and “each case must be decided on its own facts.” Du Pont, 476 F.2d at 1361, 177 USPQ at 567. In some cases, a determination that there is no likelihood of confusion may be appropriate, even where the marks are similar and the goods/services are related, because these factors are outweighed by other factors, such as differences in the relevant trade channels of the goods/services, the presence in the marketplace of a significant number of similar marks in use on similar goods/services, the existence of a valid consent agreement between the parties, or another established fact probative of the effect of use. For example, in In re Strategic Partners, Inc., 102 USPQ2d 1397 (TTAB 2012), the Board reversed a refusal to register the mark ANYWEAR (in stylized text), for “footwear,” finding no likelihood of confusion with the registered mark ANYWEAR BY JOSIE NATORI (and design), for “jackets, shirts, pants, stretch T-tops and stoles.” Given the similarity in the marks and the relatedness of the goods, the Board stated that “under usual circumstances” it would conclude that confusion is likely to occur; however, an “unusual situation” compelled the Board “to balance the similarities between the marks and goods against the facts that applicant already owns a registration for a substantially similar mark for the identical goods, and that applicant’s registration and the cited registration have coexisted for over five years.” Id. at 1399. Applicant’s prior registration of ANYWEARS for goods including footwear was substantially similar to the applied-for mark ANYWEAR for the same goods, and the registration had achieved incontestable status. Id. Basing its decision on the thirteenth du Pont factor, which “relates to ‘any other established fact probative of the effect of use,’” the Board determined that this factor outweighed the others and confusion was unlikely. Id. at 1399-1400 (quoting du Pont, 476 F.2d at 1361, 177 USPQ at 567)." In your example, the question is whether the same customers would likely be exposed to both marks, and since both are marketed to athletes, the answer is ABSOLUTELY YES. This factor is crucial as seen in TMEP 1207.01(a)(i) "In a §2(d) determination, the goods and/or services do not have to be identical or even competitive in order to find that there is a likelihood of confusion. In re Iolo Techs., LLC, 95 USPQ2d 1498, 1499 (TTAB 2010); In re G.B.I. Tile & Stone, Inc., 92 USPQ2d 1366, 1368 (TTAB 2009). The issue is not whether the goods and/or services will be confused with each other, but rather whether the public will be confused as to their source. See Recot Inc. v. M.C. Becton, 214 F.3d 1322, 1329, 54 USPQ2d 1894, 1898 (Fed. Cir. 2000) “[E]ven if the goods in question are different from, and thus not related to, one another in kind, the same goods can be related in the mind of the consuming public as to the origin of the goods. It is this sense of relatedness that matters in the likelihood of confusion analysis.”); In re Shell Oil Co., 992 F.2d 1204, 1207, 26 USPQ2d 1687, 1689 (Fed. Cir. 1993);Safety-Kleen Corp. v. Dresser Indus., Inc., 518 F.2d 1399, 1403–04, 186 USPQ 476, 480 (C.C.P.A. 1975); In re Ass’n of the U.S. Army, 85 USPQ2d 1264, 1270 (TTAB 2007). It is sufficient that the goods and/or services of the applicant and the registrant are related in some manner or that the conditions surrounding their marketing are such that they are likely to be encountered by the same persons under circumstances that, because of the marks used in connection therewith, would lead to the mistaken belief that they originate from the same source. . . .

I think my colleagues have jumped the gun. Because "Athlete" is generic for athletes [your customers] the first issue is whether the "XXX" part is sufficienty non-descriptive such that AthleteXXX can even serve as a trademark. If the "XXX" is "chat" or "web" or "talk" or "interaction" then your AthleteXXX mark is likely not registrable on the Principal Register by the Trademark Office. Which doesn't mean you can't use it as your mark, for that reason, only that you won't be able to register it [though you may be able to register it on the Supplemental Register and then move it over to the Principal Register in five years or so]. If AthleteXXX is registrable, then the next question is whether the XXX portion is so non-descriptive [that is, arbitrary or fanciful] that adding it to "Athlete" in your AthleteXXX mark will cause your customers to think about the Tourna AthleteXXX products. The more descriptive the XXX portion the less likely that mental association will be created. The more arbitrary the more likely that mental association will be created. In short, I think the decision on whether to adopt AthleteXXX as your brand identifier turns, for the most part, on how creative is the XXX portion. You simply cannot make this decision yourself. Hire a trademark attorney licensed to practice in your state [because the name of your website will be your company's trade name and trade name law is state, not federal, law]. Good luck.

Short Answer: It depends As my colleagues correctly point out, this is hard to answer without knowing the exact marks and doing some research. In general, though, you can expect the examiner to cite the "Tourna..." mark against you. You can, of course, argue and may even prevail with the examiner. In that event, you may draw an objection from the "Tourna...." mark holder. Again, this question can't be answered unless you hire an attorney who evaluates it. Good Luck.