Most sportsbooks will offer "top goalscorer" lines before and during any major football tournament, including Champions League and the World Cup.
The "top goalscorer" line is simple - you are betting on which player you think will score the most goals over the course of a tournament. There are multiple layers to betting on this line - you need to figure out which player can potentially score the most goals for a side, plus you need to figure out which team is likely to go the farthest in a tournament.
For instance, Cristiano Ronaldo will likely score a good deal of goals in the World Cup games that he plays in, though will Portugual go all the way to the finals? This is what you need to determine.
A "top goalscorer" line might look like this:
World Cup Top Goalscorer
Harry Kane, 8.00
Kylian Mbappe, 9.00
Cristiano Ronald, 13.00
Karim Benzema, 15.00
Lionel Messi, 15.00
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As you can see, there is some potential for large payouts, given that there are so many players that could potentially win the award.