Different season rewards in League of Legends can be obtained by reaching a specific rating during a Season. All ranked rewards are tied to player’s in game behavior, which means players who misbehave near the end of the Season will not be eligible for rewards, no matter their ranking.
These are the eligibility details for the Season 6: 
Riot believes that reforming from temporary bans will usually take more than just a few weeks, which is why getting temporarily suspended less than three months before the end of the season will restrict players from earning their rewards. 
Players who do not having ranked borders in the loading screen do not experience an increased amount of toxic behavior towards them. 
If a player wishes to have their ranked border removed what whatever reason, they can do so by submitting a ticket to the Player Support. 
Getting restricted from using the chat, or temporarily banned by the Instant Feedback System will also result in a Hextech Loot restriction which exceeds the duration of the punishment.
The duration of this restriction is not a fixed time. In order to regain eligibility restricted players have to show improvement of their behavior by consistently being a sportsmanlike influence in their games. 
Negative behavior during the reform period will increase the time it takes before a player can earn Hextech Loot again. 
Riot does not disclose details about the duration of the reform period.
This is intended to motivate players to truly improve their behavior,
and not just “count the days” until the restrictions vanish. 
274 https://ask.fm/RiotLyte/answers/134549636034 ; Page 2
337 https://ask.fm/RiotLyte/answers/132193089730 ; Page 122