Lamar Jackson isn't trying to trademark the number 8, Jackson (or more likely his lawyers) was contesting a particular form that Earnhardt was trying to trademark. In fact, Earnhardt said that it was a backup that they submitted in case they couldn't get the form of 8 they wanted. Since Earnhardt got the trademark for the 8 he wanted, he has already withdrawn his second submission.
https://www.msn.com/en-us/sports/motorsports/dale-earnhardt-jr-explains-why-he-gave-up-trademark-to-lamar-jackson-so-quickly/ar-AA1CCCw2
This stuff happens all the time.