If you are a professional athlete temporarily in the United States to compete in a charitable sports event, you are an exempt individual for purposes of the substantial presence test.
If you qualify to exclude days of presence as a professional athlete, temporarily in the United States to compete in a charitable sports event, you must file a fully completed Form 8843, Statement for Exempt Individuals and Individuals with a Medical Condition with the IRS.
Timely Filing of Form 8843
If you do not timely file Form 8843, you cannot exclude the days you were present in the United States as a professional athlete. This does not apply if you can show, by clear and convincing evidence, that you took reasonable actions to become aware of the filing requirements and significant steps to comply with those requirements.
Failure to timely file Form 8843 could cause a professional athlete to pass the substantial presence test. If a professional athlete passes the substantial presence test he has become a resident alien. A resident alien is subject to U.S. taxation of his entire world wide income. Thus, failure to timely file Form 8843 could result in a substantial increase in a professional athlete's U.S. tax liability.